Rainwater Harvesting - An Option to Reduce Demand on Water Supply

8/8/2019 Rainwater Harvesting - An Option to Reduce Demand on Water Supply

1/47

ENNR 429 Final Year Project

Rainwater Harvesting An Option

to Reduce Demand on Water Supply.

Final Report

Shane Phillips 81630278

Andrew Dow 15756629

06/10/08

Supervisors:

David Painter (University of Canterbury)

Katie Shorrock (MWH NZ Ltd)

Department of Civil and Natural Resources Engineering

University of Canterbury


2/47

Rainwater Harvesting An Option to Reduce Demand on Water Supply Shane PhillipsAndrew Dow

i

EXECUTIVE SUMMARY

Akaroa relies on the town water supply for their potable water. During peak demand, as wellas times of drought, water restrictions are imposed on the community. One option to help easethis problem is rainwater harvesting. Rainwater harvesting is a method of collecting

rainwater, from rooftops, to alleviate these pressures on potable water supplies.

For our final year project for Natural Resources Engineering at the University of Canterburywe have investigated the use of rainwater harvesting within the Akaroa Township. During

peak holiday times, the population of Akaroa can swell to more than twice its original size,putting pressure on local amenities, in particular the already restricted domestic water supply.The current water management practices imposed during water restriction times have asignificant impact in conserving water and reducing demand. Imposing Level 1 restrictions,i.e. alternate day watering, can reduce demand by around 17%, whilst imposing Level 4restrictions, i.e. a total hosing ban, can deliver around a 52% reduction in water demand(Shorrock, 2008). Rainwater harvesting may provide a major part of the solution to water

problems in Akaroa.

The idea for this project was borne out of discussions with Katie Shorrock, MWH, duringShane Phillips summer internship. Katie was working on the Akaroa Water ManagementStrategy developing options for alternative sources of potable water to reduce the demand onthe Akaroa potable water supply. Our investigation is intended to complement the workcarried out by MWH and provide CCC with a detailed case study on rainwater harvesting thatis specific to Akaroa.

While looking at the feasibility of the rainwater tank, we also investigated the benefitsrainwater harvesting can provide to the community and the local council. These benefits are

closely aligned with the issues and actions raised in the Greater Christchurch UrbanDevelopment Strategy 2007 (Chapter 6.23 Water Supply). In addition, we endeavoured to

provide the most effective solution.

A comprehensive literature review has been carried out on rainwater harvesting. The reviewfocuses primarily on current applications of rainwater tanks within New Zealand, focussingon examples of rainwater tanks in use in New Zealand, end use of roof water, incentives,

behavioural considerations, water quality and treatment, components of a rainwater harvestingsystem and installation.

We acquired funding for the project from Christchurch City Council in the order of $1,500,

and Liz Mars, a resident living on Beach Rd, Akaroa kindly volunteered for a rainwater tankto be installed on her property. Prior to installing the rainwater harvesting system we carriedout a current consumption (baseline) study throughout the month of June, to give us anindication of the current potable water consumption at the Mars residence. The total volumeof potable water used throughout this period was 12,410 litres.

The rainwater harvesting system was installed at the Mars residence on Thursday 26 June2008, in accordance with the manufacturing instructions. The system is intended to be utilisedfor external purposes in place of the reticulated domestic system. Following this, weundertook a three month data collection period from July to September. Throughout this datacollection period Liz Mars was recording:

The 24-hour rainfall depth from the rain gauge

The level within the tank from the clear tank level indicator


3/47


ii

The flow meter at her property boundary

The total rainfall during the July to September period was above average and the winterperiod (June to August) could be classified as a wet winter. However, as the rainfall volumeswere within one standard deviation from the mean they can be classified as typical rainfall

volumes for Akaroa

The total potential volume of rainwater that could have been collected during out testingperiod was 28.44 m. However, due to the constant adverse weather conditions the rainwatertank was full for the majority of this period, so most of that volume would have flowed downthe tank overflow pipe, and into the domestic storm water system.

The total volume of collected water used during our three month period was 13.46 m.However, this value is not indicative of actual consumption as the majority of this water wasused by Liz either to ensure the system was working correctly, or just flushed down thedomestic storm water pipe to provide variability in our readings, allowing us to ensure our

calculations and data analysis were accurate.

The water quality tests show an overall positive result. Two determinands showed valuesoutside of the maximum acceptable values (MAV) outlined by the Ministry of Health. Totalcoliforms were unacceptable and the pH (6.3) was reasonable but outside of the recommendedrange of 7 8.5.

Unfortunately, due to the incredibly wet winter very little water was actually used from thesystem productively in place of potable water. As a consequence we could not get the resultsrequired to effectively quantify a reduction in potable water demand. However, as theChristchurch City Council requires a twelve month study it is our recommendation that the

data we have collected be used as a four month baseline period and a twelve month study iscontinued henceforth. Also, for the collected rainwater to be maximised to its fullest potentiala pump is required for the system.

We believe that rainwater harvesting is an underutilised, alternative source of water. It can beused in place of potable water for uses such as: garden watering, car and boat washing, orfilling pools, spas and ornamental ponds. The use of alternative water sources such as roof-collected rainwater is definitely part of the solution to diminishing water resources (Abbot,2007).


4/47


iii

NOTATION

The following symbols and abbreviations are used throughout this report:

V Volume (m)

RoofA Roof Area (m)

ageAnnualAverV Annual Average Rainfall Depth (mm)


5/47


iv

TABLE OF CONTENTS

1.0 AKAROA SETTING THE SCENE.........................................................................1

2.0 AIMS AND OBJECTIVES..........................................................................................3

3.0 LITERATURE REVIEW............................................................................................3

3.1 Rainwater Tanks Use in New Zealand ...................................................................3

3.2 End Use......................................................................................................................3

3.3 Council Incentives ....................................................................................................43.3.1 Subsidy ...............................................................................................................43.3.2 Tax and Cost Rebate...........................................................................................43.3.3 Rebates ...............................................................................................................53.3.4 Education and Raising Awareness .....................................................................53.3.5 Guidelines...........................................................................................................53.3.6 Restriction in Usage ...........................................................................................5

3.4 Behavioural Considerations ....................................................................................63.4.1 Human Behaviour...............................................................................................63.4.2 Climate Change ..................................................................................................6

3.5 Water Quality ...........................................................................................................63.5.1 Contaminant Sources..........................................................................................63.5.2 Methods to Improve Water Quality....................................................................7

3.6 Components of a Rainwater Harvesting System...................................................83.6.1 Gutters and Downpipes ......................................................................................93.6.2 First Flush...........................................................................................................93.6.3 Pipes ...................................................................................................................9

3.6.4 Storage Tanks .....................................................................................................9

3.7 Installation...............................................................................................................103.7.1 Site Preparation ................................................................................................103.7.2 Plumbing...........................................................................................................103.7.3 Consents ...........................................................................................................11

4.0 BUDGET .....................................................................................................................12

5.0 TIMEFRAME.............................................................................................................12

5.1 Project Proposal and Presentation........................................................................13

5.2 Meet with CCC .......................................................................................................135.3 Establish Location ..................................................................................................13

5.4 Baseline Monitoring Period ...................................................................................14

5.5 Construct Rainwater Harvesting System.............................................................14

5.6 Daily Water Measurements...................................................................................14

5.7 Final Report ............................................................................................................14

6.0 METHODOLOGY.....................................................................................................15

6.1 Selection of Location ..............................................................................................15

6.2 Sizing of Tank .........................................................................................................16

6.3 Installation of Rainwater Harvesting System ......................................................18


6/47


v

6.4 Data Collection........................................................................................................206.4.1 Baseline Monitoring .........................................................................................206.4.2 Results Collection.............................................................................................20

6.5 Data Analysis ..........................................................................................................21

6.6 Water Quality Test .................................................................................................217.0 RESULTS....................................................................................................................22

7.1 Akaroa Rainfall ......................................................................................................22

7.2 Rainwater Harvesting System...............................................................................237.2.1 Baseline Period .................................................................................................237.2.2 Rainfall .............................................................................................................247.2.3 Flow Meter .......................................................................................................257.2.4 Rainwater Harvesting System ..........................................................................26

7.3 Water Quality Testing............................................................................................27

8.0 DISCUSSION..............................................................................................................30

8.1 Rainwater Harvesting System...............................................................................30

8.2 Water Quality Test .................................................................................................318.2.1 Physical Appearance.........................................................................................318.2.2 Effect from Salt Spray ......................................................................................328.2.3 Butynol Roofing ...............................................................................................328.2.4 Water Quality Improvements ...........................................................................32

8.3 Human Behavioral Response.................................................................................32

9.0 CONCLUSIONS AND RECOMMENDATIONS ...................................................35

9.1 Options for Further Study.....................................................................................36

10.0 ACKNOWLEDGEMENTS .......................................................................................37

11.0 REFERENCES ...........................................................................................................38

12.0 APPENDICES.............................................................................................................40

APPENDICES

APPENDIX A MICO PIPELINES RAIN HARVESTING SYSTEMS BROCHURE

APPENDIX B RX PLASTICS SITE PREPARATION AND TANK INSTALLATION

APPENDIX C PROJECT TIMELINE

APPENDIX D INITIAL COUNCIL CORRESPONDENCE

APPENDIX E AVERAGE ANNUAL RAINFALL

APPENDIX F MICO PIPELINES INVOICE

APPENDIX G HILL LABORATORIES TEST RESULTS

APPENDIX H RAINWATER HARVESTING SPECIFICATION


7/47


vi

TABLES

Table 1 - 2004 - 2041 Population and Demand Data for Akaroa...............................................2

Table 2 - Future Demand Figures for Akaroa under Varying Degrees of Restrictions..............2

Table 3 - Total Required Costs.................................................................................................12Table 4 - Total Project Costs ....................................................................................................12

Table 5 - Potential Rainfall Volume Available ........................................................................25

Table 6 - Rainwater Volume Used ...........................................................................................26

Table 7 - Water Quality Test Results .......................................................................................29

FIGURES

Figure 1 Mars Residence .......................................................................................................15

Figure 2 NIWA Rain Station.................................................................................................16

Figure 3 Total Annual Rainfall..............................................................................................16

Figure 4 Area of Roof Catchment .........................................................................................17

Figure 5 Mars Roof ...............................................................................................................17

Figure 6 Conceptual Outlay of System .................................................................................18

Figure 7 Path to Tank ............................................................................................................19

Figure 8 Leaf Slide ................................................................................................................19

Figure 9 Rainwater Harvesting System.................................................................................19

Figure 10 Leaky Fitting .........................................................................................................20

Figure 11 Flow Meter ............................................................................................................20

Figure 12 Monthly Average Rainfall.....................................................................................22

Figure 13 Daily Water Use (June).........................................................................................23

Figure 14 Rain Gauge............................................................................................................24

Figure 15 Monthly Rainfall ...................................................................................................24

Figure 16 Monthly Potable Water Use..................................................................................25

Figure 17 Clear Tank Level Indicator ...................................................................................26

Figure 18 Rainwater Usage ...................................................................................................27

Figure 19 Water Samples ......................................................................................................28

Figure 20 Tank Water Surface...............................................................................................32


8/47


1

1.0 AKAROA SETTING THE SCENE

The township of Akaroa on Banks Peninsula has a long history of water shortages. Theresidents of Akaroa currently rely on the town water supply for their potable water. During

peak holiday times, the population of Akaroa can swell to more than twice its original size,

putting pressure on local amenities, in particular the already restricted domestic water supply.One option to help ease this problem is rainwater harvesting. Rainwater harvesting is amethod of collecting rainwater, from rooftops, to alleviate these pressures on potable watersupplies. The benefits of rainwater harvesting include:

A primary financial benefit of rainwater tanks to the community (in contrast to theindividual property owner) is the potential reduction in the cost of water and stormwater infrastructure

A reduction in demand for mains water supply, resulting in a reduction in rates wheredomestic water is charged

A reduction in flooding by providing temporary storage for rainwater A reduction in wet weather sewage overflows

A reduction in stormwater pollution of our beaches and waterways.

The idea for this project was borne out of discussions with Katie Shorrock, MWH, duringShane Phillips summer internship. Katie was working on the Akaroa Water ManagementStrategy developing options for alternative sources of potable water to reduce the demand onthe Akaroa potable water supply. During exceptionally dry years the Christchurch CityCouncil (CCC) has often relied on the goodwill of the Akaroa community to conserve waterwhere possible and there have been periods extending to several months where no water has

been available for non-essential uses such as garden watering.

The population of Akaroa is steadily-increasing. This means that management of the existingwater source alone can no longer provide an acceptable level of security of the water supply.As a result the CCC is investigating options to alleviate demand and potentially providealternative sources of potable water.

Table 1 shows the 2004 and projected 2041 population data for Akaroa. The population datahave been taken from the Akaroa Water Management Strategy Part 4: Water Supply andTreatment Options (Shorrock, 2008) and the 2041 projections are based on the 2026

population figures in the same report with a 9% growth rate as per the Greater Christchurch

Urban Development Strategy. These figures are the maximum values and therefore representthe worst-case scenario.


9/47


2

Table 1 - 2004 - 2041 Population and Demand Data for Akaroa (MWH NZ Ltd)

Peak UnitDemand

l/(pers.day)

Current2004

Future2041

MaximumPopulation

PeakDemandm/day

MaximumPopulation

PeakDemandm/day

Residential 713 650 463 930 663

Holiday Homes 565 2,200 1243 2940 1661

Commercial 200 800 160 1850 370

Overnight Friends 200 80 16 190 38

Day Visitors 15 2,500 38 9810 147

Losses 15% - 282 - 473

Total 2202 3311

Demand figures have been calculated by multiplying the population figures by the peak unitdemand. The peak unit demand for each population category was calculated based on typicalusage data (Christchurch City Council, 2007). The current water management practicesimposed annually during water restriction times have a significant impact in conserving waterand reducing demand. Imposing Level 1 restrictions, i.e. alternate day watering, can reducedemand by around 17%, whilst imposing Level 4 restrictions, i.e. a total hosing ban, candeliver around a 52% reduction in water demand (Shorrock, 2008). Rainwater harvesting may

provide part of the solution to water problems in Akaroa. The effect of water restrictions onthe demand is illustrated in Table 2.

Table 2 - Future Demand Figures for Akaroa under Varying Degrees of Restrictions

(MWH NZ Ltd.)

CurrentDemand(m/day)

FutureDemand(m/day)

Future Demandunder Level 1

Restrictions(m/day)

Future Demandunder Level 4

Restrictions(m/day)

Akaroa 2202 3311 2748 1589

Our investigation is intended to complement the work carried out by MWH and provide CCCwith a detailed case study on rainwater harvesting that is specific to Akaroa. The findings ofthe research will be used to assess the viability of using rainwater harvesting as a method to

ease the strain on potable water resources in Akaroa. In addition, the model could be appliedto other similar rural settings within New Zealand and improve the way we use our naturalresources. An investigation has been made into the uses of the rainwater and also into thecosts and benefits of different rainwater systems.


10/47


3

2.0 AIMS AND OBJECTIVES

The aims and objectives of this project, as set out in our project proposal are:

To install a rainwater harvesting system at a selected location in Akaroa

To quantify the percentage reduction in demand for potable water as a direct result ofinstalling a rain water harvesting system

To assess the quality of the water and whether or not that affects the end-use

To produce a specification for a low-cost, easy-to-use rainwater harvesting packagewith costs.

3.0 LITERATURE REVIEW

A comprehensive literature review has been carried out on rainwater harvesting. The reviewfocuses primarily on current applications of rainwater tanks in New Zealand and covers thefollowing areas:

Examples of rainwater tanks in use in New Zealand

End use of roof water

Incentives

Behavioural considerations

Water quality and treatment

Components of a rainwater harvesting system

Installation.

3.1 Rainwater Tanks Use in New Zealand

Rainwater harvesting systems have been encouraged throughout New Zealand throughCouncils such as the North Shore, Rodney, Waitakere and Kapiti. These city and districtcouncils have encouraged rainwater harvesting by providing subsidies and incentives to

homeowners to install and use rainwater harvesting systems. Waitakere City Council has beenat the forefront of such changes by providing $500 rebates for homeowners that installrainwater tanks. North Shore City Council and the Rodney District Council have also

provided $500 subsidies. Further details of the current rainwater harvesting practices in theaforementioned Councils are provided throughout the literature review.

3.2 End Use

In extreme cases, rainwater can supply up to 65% of a domestic households water (Waitakere

City Council, 2008). It can be used for:

Watering the garden and lawn


11/47


4

Washing vehicles and boats

Supplying the laundry and toilet

Topping up spas, ornamental ponds and swimming pools.

3.3 Council Incentives

Economic incentives for rainwater harvesting can be classified (Mohd Shahwahid et al., 2006)as follows:

i) Provision of subsidies

ii) Tax and cost rebates

iii) Rebates

iv) Education and raising awarenessv) Guidelines

vi) Restriction in usage of piped water.

3.3.1 SubsidyIn Malaysia it has been discovered that the cost of installation, maintenance and usage ofrainwater harvesting exceeds the cost of the reticulated water supply (Mohd Shahwahid et al.,2006). As a result, they are looking at providing subsidies to rainwater harvesting systems andservices.

Similarly, in Queensland, Australia, the government has introduced a new programme, theHome WaterWise Service, which is a subsidized plumbing service that amongst other services

provides water audits to homeowners. This could be applied in Akaroa in several measures,including:

i) Providing water audits to homeowners,

ii) Providing subsidised rainwater harvesting installation.

3.3.2 Tax and Cost RebateAnother economic initiative used to encourage the use of rainwater harvesting is to put in

place tax rebates for both homeowners and manufacturers and suppliers of rainwaterharvesting systems.

Rainwater harvesting can be integrated with the existing water supply which will result in lessdemand on the existing water supply. A tax rebate could be provided to compensate thosehomeowners that are using less of the existing water supply. This is simply a transfer of the

benefit to the homeowner.

Further, as there is a relatively short supply of manufacturers and suppliers of rainwaterharvesting, a tax rebate has the potential to encourage entry into the market. There is space in

the market for rainwater harvesting. For instance, the Waitakere City Council is finding itdifficult, due to the lack of commercial supply, to implement a scheme to encourage the useof rain barrels as a smaller alternative of water supply for irrigation purposes. To encourage


12/47


5

the manufacturers and suppliers of rainwater harvesting equipment a tax rebate could be putin place to encourage a competitive market. Another example is that in Texas, USA, SalesTax Redemption has been offered on all water efficiency equipment, including rainwaterharvesting equipment (Texas Water Development Board, 2008).

3.3.3

Rebates

The provision of rebates has been the primary way in which the current rainwater harvestingadvocates have promoted installation and use of rainwater systems. North Shore City Council

provides a $500 rebate to homeowners who install and use rainwater harvesting. Similarschemes have been implemented in Australia with rebates up to $800 given in Sydney and inToowoomba rebates of $500 are given. Each place has conditions on the rebates. For instancein Toowoomba, to be eligible for the rebate the tank must have a capacity of 5,000 litres. InSydney, the eligibility is based on the size of the tank and also if it is connected to the toilet orwashing machine (Sydney Water, 2008).

3.3.4 Education and Raising AwarenessEducation and raising awareness is a key initiative to encourage the use of rainwaterharvesting. Waitakere City Council has a series of brochures produced to educate the publicon rainwater harvesting. National Hydraulic Research Institute of Malaysia (NAHRIM)suggests that the use of rainwater harvesting should be incorporated in the school educationcurriculum.

In Australia, certain state governments have introduced a rainwater tanks in schools programme where participating schools are given rebates on rainwater harvesting systems.Also, awareness campaigns are carried out in participating schools on the importance of

conserving water (Sydney Water, 2008).

3.3.5 GuidelinesWith guidelines in place, homeowners are more likely to move towards rainwater harvesting.Appropriate guidelines will make rainwater harvesting more efficient as homeowners willinstall the proper and most suitable rainwater harvesting system.

The Cooperative Research Centre for Water Quality and Treatment in Australia published amanual to assist the water industry to integrate rainwater harvesting systems into the urbanenvironment. The manual outlines the appropriate end uses, tank sizing, site design, collection

process, and conveyance from roof to tank, maintenance procedures and other issues involvedwith rainwater tanks (Chapman et al., 2008).

3.3.6 Restriction in UsageAnother economic instrument to encourage rainwater harvesting is to restrict the use of pipedwater. Water restrictions are already imposed in Akaroa.


13/47


6

3.4 Behavioural Considerations

3.4.1 Human BehaviourRainwater harvesting is a change from the central water supply scheme to either an individual

or combined alternative water supply. However, it is not only a physical change but itincludes aspects of social and economic change. Rainwater harvesting can be promoted as asustainable water supply that also significantly improves the lifestyles of people in thecommunity. There has been a paradigm shift in peoples behavior more towards the greenapproach to everyday commodities.

Installing a rainwater harvesting system in a home is the first step. However, making thesystem as readily available and useable as the existing water supply is the next step.

The principles of the Treaty of Waitangi must be taken into consideration in decision-makingunder the Resource Management Act (1991). Maori spiritual values are a primary concern of

the Treaty of Waitangi. Maori believe that water has a spiritual link to the past. Inenvironmental, cultural, social, and economic terms, sustainable urban water infrastructureshould be developed and operated in harmony with natural water cycles and water catchments(Morgan, 2005). This aligns to the rainwater harvesting procedures and techniques.

3.4.2 Climate ChangeClimate change will cause a general intensification of the earths hydrological cycle. In thenext 100 years it is expected that there will be an increase in precipitation, evapotranspiration,occurrence of storms and significant changes in the chemical processes that influence waterquality (Mohd Shahwahid et al., 2006). In short, this means the consistencies of having water

supply will be under threat. There is a need for greater storage capacity to cope during the dryperiods. Rainwater harvesting may be part of the solution, as the rain can be collected over theshorter rainfall times and stored for the time when there is a shortage of water.

3.5 Water Quality

The quality of rainwater is generally perceived as pure because it has come from the sky.This idea has been challenged by research into waterborne diseases that have become more

prominent as rainwater harvesting becomes more popular. The microbiological quality of

water is the most important factor to test for in determining the safety of water supplies from ahealth perspective.

3.5.1 Contaminant SourcesThe primary sources of contaminants for roof water are the algae and bacteria that can growin the system. This is of concern, but can be prevented; prevention methods are detailed in alater section. A five-year Massey University study was completed investigating themicrobiological quality of roof water. 560 private dwellings were tested over the five-year

period and over half of the samples analysed exceeded the acceptable standards forcontamination. In more than 30% of the samples there was evidence of heavy faecal

contamination. The source of the contamination can be attributed to birds, frogs, possums,rodents, and dead animals and insects either on the roof or in the gutters, or in the water tankitself. The samples showing a large amount of contaminants were primarily in under-utilised


14/47


7

systems where there was lack of maintenance. Also, in these tanks there was evidence ofinadequate disinfection, poorly designed delivery systems and storage tanks, and a failure toadopt even simple physical measures to safeguard the water.

Stan Abbot of the Roof Water Research Centre at Massey University, Wellington, reports that

New Zealand studies show that consumption of roof-collected water is associated with athreefold greater risk of campylobacteriosis than that of non-consumers. Also, in a casecontrol study on risk factors for giardiasis among children in Auckland, it was found thatconsumption of roof-collected rainwater significantly increased the risk for this infection.

The drinking water standards of New Zealand (DWSNZ) have several requirements that mustbe fulfilled. The DWSNZ describe the microbiological factors in rainwater in particular, withreference to minimising the enteric pathogens, including types of bacteria such as Salmonellaand Campylobacter and protozoa such as Cryptosporidium and Giardia. The likely sources ofthese contaminants are from animals in the gutters or in the tank itself (Ministry of Health

New Zealand, 2005).

The DWSNZ also describe the chemistry of rainwater, including what can lead to changes inthe chemicals in rainwater. Lead in rainwater can be attributed to motor vehicle fumes, withother contaminants identified from high-density roads being nitrate, copper, nickel, cadmiumand zinc (Ministry of Health New Zealand, 2005)

Smoke from chimneys is seen as a source of contaminants. Some of the smoke and sootsettles on the roof and this is later washed off by the rain. Some researchers have related thehigh incidence of stomach cancers in part of Iceland to the presence of polyaromatichydrocarbons in rainwater (Dungal, 1961). Storage materials and the effect of nearby trees isalso seen as a potential source of contaminants. The effect of nearby trees can lower the pH

below 6 but the primary concern is the leaves providing detritus that feed bacterial growth inthe tank.

3.5.2 Methods to Improve Water QualityAs rainwater harvesting becomes a more popular source of water supply there has beenongoing research into the improvement of water quality. Testing of these systems is out of thescope of this research but it is worthwhile noting the developed systems and theireffectiveness in improving water quality.

Once the rainwater lands, its quality will be affected by the roof, gutters and storage system.

Water does not stay on the roof for long so it is said to not have a marked effect on the waterquality, with the few exceptions being a newly painted roof and an unpainted galvanised steelroof, which will lose zinc for months (Ministry of Health New Zealand, 2005).

Stan Abbott (2006) concludes that the quality of the water improves dramatically with the useof first-flush diverters. The purpose of the study was to establish which products and systemswere effective in providing a safeguard against the contaminants collected on the roof. The

project was set up with six rainwater tank systems with various screens and first-flushdiverters. There were 25 sampling events over a period of 9 months and the Total Coliformsand Escherichia coli were tested. The First-Flush Water Diverter consistently yielded low tozero counts of both Total Coliforms and Escherichia coli, in contrast to the samples taken in

the first-flush diverter where the Total coliforms were high but the Escherichia coli were notso high (Abbott, 2006).


15/47


8

Additives for settling sediments or buffering pH and simple filters are optional treatments fornon-potable uses of rainwater. Fine filters and microbiological disinfection are only necessaryfor drinking water.

It is important to note that water quality may be affected by dirt, rust, lime scale, bird and

rodent droppings, and airborne bacteria and algae may still enter the tank even when primaryscreening and first-flush diverters are in place. Even for non-drinking uses, sedimentation ofsuspended solids inside the tank and further filtration are a good idea.

Fine filters may be installed prior to the end use, e.g. at the washing machine and toiletcistern. Simple cartridge filters similar to those used for domestic swimming pools or hot tubsare suitable (e.g. 80 micron washable filters) (Waitakere City Council, 2008).

In rainwater systems the emphasis is on the maintenance of the whole system to preventcontamination rather than treatment prior to end use. Waitakere City Council is a forerunnerin encouraging rainwater harvesting. They provide the public with general tips on keeping

water safe (Waitakere City Council, 2008). These include:

A tight fitting top cover on the storage tank to keep mosquitoes and animals out aswell as preventing evaporation

Locate storage tank in a cool place, out of sunlight to discourage the growth of algae

Use safe roof paint suitable for roof water

Inspect gutters regularly and clean them out if necessary

Keep the roof clear of overhanging vegetation

Install removable gutter guards if appropriate

Inspect tank annually and if required get it cleaned out by a professional

Use a backflow prevention device to stop contaminated water from flowing back intothe mains water supply in a dual system.

Treatment of rainwater can be avoided by following preventative measures and maintainingeach component of the rainwater harvesting system. However, if treatment is required, theroof water quality can be improved by:

Boiling water

under-the-bench filters

UV disinfection units.

3.6 Components of a Rainwater Harvesting System

Rainwater harvesting systems have been developed with several additional components. Forthis project we have used only the essential components required.


16/47


9

3.6.1 Gutters and DownpipesSeamless extruded Aluminium, galvanised steel or PVC are commonly recommended forgutters and downpipes. Copper is also used; however, it is quite expensive and increasinglylikely to be stolen. Gutters and downpipes must be properly sized, sloped and installed to

maximise the quantity of rainwater collected.

Leaf guards are the primary screening devices designed to prevent leaves and other debrisfrom entering the rainwater harvesting system. They attach to the gutter and typically have a 4mm mesh to keep out leaves and debris(Marley, 2008).

3.6.2 First FlushFirst-flush diverters direct the first runoff from a roof after rainfall into a separate smallchamber because this water collects most of the dirt, debris and contaminants. Typically 40litres for every 100 m of roof area is diverted. Once the chamber has filled, the rest of the

water flows to the downpipe connected to the rainwater tank. The small chamber has a smalltube in it that allows it to empty itself before the next rainfall event (North Shore CityCouncil, 2008).

Generally, first-flush diverters are an optional item for systems where the end use is non-drinking water.

3.6.3 PipesEffective plumbing is important for efficient rainwater collection and to protect the householdor mains water supply from contamination. Debris needs to be diverted and backflow

preventers may need to be installed. It is recommended that all plumbing be carried out by aqualified plumber so that recognised plumbing standards are met.

3.6.4 Storage TanksTanks come in a variety of different sizes, and even small tanks can provide significantquantities of water for use around the house.

There are different types, styles and shapes of tanks available. The most common arepolyethylene or concrete and they can be installed either above or below ground. Putting thetank underground is a good option for urban dwellers with smaller sections.

There are a lot of options available in tank materials, including:

Polyethylene

Timber

Steel

Concrete

Fibreglass.

The tank should have a durable, watertight, opaque exterior and a clean, smooth interior. Atight-fitting top cover is to prevent evaporation, mosquito breeding and keep insects, rodents,birds and children out of the tank. It is best to locate the tank in a cool place, out of sunlight,


17/47


10

so that algae do not grow. A suitable overflow outlet and access for cleaning are alsoimportant. The tank should be placed high enough for gravity to convey the water or be fittedwith a pump.

The rainwater tank size will depend on:

The volume of water needed

The amount and pattern of rainfall

The area of the collection surface

The security of the supply needed.

A full and comprehensive list of the available fittings and attachments for rainwaterharvesting systems can be found in the appendices (Appendix A Mico Pipelines RainHarvesting Systems Brochure).

3.7 Installation

The installation of the tanks is generally the responsibility of the owner, not the supplier.However, both manufacturers and suppliers produce recommendations and guidelines for theinstallation of water tanks. A copy of the installation instructions provided by RX Plastics can

be found in the Appendices (Appendix B RX Plastics Site Preparation and TankInstallation).

3.7.1 Site PreparationThe site should be firm, level, stable ground that adequately and uniformly supports the baseof the tank over its whole area. The area should be free from any sharp objects such as stonesor roots. If the tank foundation is cutting into a sloping section care needs to be taken toensure that the area will not erode. If a tank stand is used the planks should not be spacedmore than 10 mm apart (Bailey Tanks, 2008).

3.7.2 PlumbingIt is recommended that all plumbing is carried out by a registered plumber to ensure that itcomplies with the New Zealand Building Code. This states that:

Any connection between the tank and a pump should include a flexible hose to absorbvibration

Pipe work between tanks or rigid structures should include a flexible hose or a 90-degree loop to allow for expansion or shrinkage with temperature changes

The overflow should be piped away from the foundation to prevent erosion.

Also, the Bailey Tank Installation Instructions recommend the use of an appropriate-sizedholesaw to cut the hole for inlets and outlets. It also recommends avoidance of chisels and

punches.


18/47


11

3.7.3 ConsentsA building consent is not generally required for tanks used only for garden irrigation. A

building consent is required for any tank connected to household plumbing (Waitakere CityCouncil, 2008).

This includes rainwater collection systems that:

Connect to the mains water system as a backup and therefore require a backflowprevention device

Exceed 25,000 litres capacity and are supported directly on the ground

Exceed 2,000 litres capacity and are supported more than two metres above theground

Exceed 500 litres capacity and are supported more than four metres above theground.

Tanks larger than 6,000 litres may require resource consent to ensure that they meet certaincriteria such as distances in relation to boundary, etc. (Waitakere City Council, 2008).


19/47


12

4.0 BUDGET

We initially obtained funding to a value of $1,500 for this project from Christchurch CityCouncil (Contact: Simon Collin, CW and W Network Planning). The value of $1,500 waschosen as we thought that would be a sufficient amount to carry out the project given that we

had no prior experience with the price of rainwater harvesting systems. The total costs for theproject were:

Table 3 - Total Required Costs

Item Number Price Cost

90 80 mm uPVC bend 2 $4.01 $8.02

3 m length 80 mm uPVC pipe 4 $21.96 $87.84

90 50 mm LDPE bend 2 $20.99 $41.98

25 m coil 50 mm alkathene pipe 1 $84.92 $84.92

20 mm polyethylene tank connector 1 $3.85 $3.85

20 mm BSP ball valve 1 $10.09 $10.0920 mm sprinkler adaptor 1 $1.62 $1.62

Leaf Slide 1 $71.16 $71.16

3200L PE Foam Tank 1 $1,095.00 $1,095.00

90 25 mm LDPE bend 2 $14.99 $29.98

25 m coil 25 mm clear tubing 1 $38.98 $38.98

Water Sampling and Testing 1 $344.24 $344.24

Personnel Hours Price Cost

Research Facilitators 480 $0.00 $0.00

David Painter 30 $0.00 $0.00MWH NZ Ltd 12 $0.00 $0.00

Christchurch City Council 5 $0.00 $0.00

Subtotal $1,817.68

GST $227.21

Total $2,044.89

From Table 3, it can be seen that the total required cost of the project exceeds the allocated project budget. This is not an issue however, as we were able to procure a 3,200 litre RXPlastics foam tank, worth $1,095, at no cost. The total value actually spent on the project,

from the $1,500 budget is shown in Table 4.

Table 4 - Total Project Costs

Mico's $309.48

Hill's Lab $344.24

Subtotal $653.72

GST $81.72

Total $735.44

This is well within our allocated budget and leaves $746.56 still available. Possible uses forthis surplus are discussed in Section 9.1 Options for Further Study.


20/47


13

5.0 TIMEFRAME

A complete project timeline can be seen in the Appendices (Appendix C Project Timeline),the key components of which are discussed in detail below.

5.1 Project Proposal and Presentation

The project proposal and presentation was on Wednesday 19 March. The feedback from theproposal has been incorporated into this report.

5.2 Meet with CCC

Following initial correspondence with Simon Collin (CCC) (Appendix D Initial Council

Correspondence); we met with him on Friday 4 April 2008 to discuss the project in detail.The purpose of the meeting was to confirm that we were meeting the Councils expectationsof the project and attempt to acquire financial backing to fund our study.

The Council recommendations following this meeting were as follow:

Each residential property within Akaroa has a flow meter, so we do not need to purchase and install one for the purpose of our baseline monitoring period. Thisbaseline monitoring period will consist of daily readings of the flow meter to measurethe current water consumption.

A rain gauge would be required at the selected location. This would provide us withexact data and would be more readily available than National Institute for Water andAtmosphere (NIWA) CliFlo data which are updated only periodically.

A newer house would be preferred for the study as, being built from modern materials,it would give a more accurate representation of the kinds of contaminants that can becollected in rainwater from modern buildings.

Ken Paulin, a retired engineer living in Akaroa, could be a possibility for the locationof the rainwater harvesting system.

The Council also wanted assurance that the study would continue for 12 months, asthis would give them the most accurate set of data to quantify reduction in potablewater demand. This was to be confirmed with Canterbury University and MWH NZLtd.

As a result of the meeting we were allocated a $1,500 budget for the purpose of our study.

5.3 Establish Location

A location has been established within Akaroa. Liz Mars, a resident living on Beach Rd,Akaroa has kindly volunteered for a rainwater tank to be installed on her property. Details of

her property are further discussed in the methodology, Section 6.1 Selection of Location.


21/47


14

5.4 Baseline Monitoring Period

With the location selected for the rainwater harvesting system, it was then possible to proceedwith the baseline monitoring period. It was intended to monitor the current consumption at thechosen site for one month prior to installing the rainwater harvesting system. As mentioned

earlier, Akaroa is already on flow meters so we did not have to install one for the purpose ofour study.

The data collection for the baseline monitoring was done by Liz Mars and consisted of herreading and recording the consumption at the flow meter at her property boundary on a daily

basis from 1 June to 30 June 2008. This provided us with a baseline for current potable waterconsumption at her property.

5.5 Construct Rainwater Harvesting System

The system was installed at the Mars property on Thursday 26 June 2008, prior to completionof the baseline monitoring period. This was a major milestone for our project as it signifiedthe commencement of the measurement and sampling period. Details of the installation

process can be found in Section 6.3 Installation of Rainwater Harvesting System.

5.6 Daily Water Measurements

Daily water measurements commenced from Tuesday 1 July 2008 and will continue fortwelve months. The measurements are being carried out by Liz Mars and the data are being

forwarded to us on Wednesday of each week. Details of this data collection are in Section 6.4Data Collection. We then analysed the data and recorded the results for this final report. Thisanalysis can be found in Section 6.5 Data Analysis.

5.7 Final Report

This final report was due on Monday 6 October 2008. It includes a summary, literaturereview, our methodology, data, analysis, results, discussion, conclusions andrecommendations. Copies of this report will be presented to MWH NZ Ltd and the

Christchurch City Council.

For the purpose of this Final Report, the daily water measurements continued until Tuesday30 September. This covered approximately a three-month period for our analysis. It hasfurther been proposed that, for the benefit of the Council, the data collection will continueuntil 30 June 2009. It is proposed that the project be continued by MWH NZ Ltds summerintern over the summer months, and students in their Final Year of Natural ResourcesEngineering in 2009, to give the Council the complete 12-month study they requested. A fulldata analysis will also be carried out over this period.


22/47


15

6.0 METHODOLOGY

The methodology for our project is as follows:

Selection of Location

Sizing of Tank

Data Collection

Water Quality Test

Data Analysis

Data Communication

Each of these items is discussed in further detail below.

6.1 Selection of Location

After initial discussions with both MWH NZ Ltd and Christchurch City Council, Ken Paulin,a retired engineer living in Akaroa, was identified as a possible candidate for allowing thestudy to be undertaken at his residence. Following contact with Ken it was decided not to usehis property as he would be away for the majority of June and July, right through our initialmonitoring period. However, he did offer to talk to a few locals within Akaroa and see ifanyone was interested.

As a result of Kens investigations he passed

on to us the contact details of Liz Mars. Lizwas intending to install a rainwater harvestingsystem at her property in the near future. Lizs

property, located at 259 Beach Rd, (Figure 1)seemed an ideal location for our study. TheMars residence is a three-bedroom, two-storey

building with a total roof area of 111 m2. Thehouse is of modern construction with a plasterand Coloursteel exterior and a butynol roof.This was seen as typical of properties withinAkaroa and as a result was selected as the

location for our study.

There is already a rain gauge at the Mars Residence as Liz monitors the current rainfall for herown personal interest. This means that we did not have to purchase a rain gauge as a part ofthe rainwater harvesting system for the purpose of our study.

Lizs only concern was that she would be away from 3 June to 7 June 2008, but could getsomeone to come and take the readings for her. Also, as the most probable location of the tankon her property is in a garden of New Zealand native plants, she wanted the lancewood andkowhai trees left alone, whereas all other plants could be removed or relocated.

Figure 1 - Mars Residence (Liz Mars)


23/47


16

6.2 Sizing of Tank

The major design component of the rainwater harvesting system is the size of the tank. Thetank must be sized to adequately store the collected roof runoff without being too big, and so

be nearly empty a lot of the time, or too small, and be nearly full all the time.

To size the tank, first we needed to knowthe total amount of expected rainfall for theregion. To do this we selected a NIWA rainstation close to our chosen site. (Figure 2).The Rain station chosen was the OnukuWeather Station (Latitude -43.843,Longitude 172.962). It was selected as it isthe closest rain station to the Mars propertyand Liz had previously indicated that due tothe geography of Akaroa the peninsula

where her house was situated was drier thanthe township. With this weather stationselected, we were able to download theCliFlo daily rainfall records dating back to1 January 1963. These were then analysedand put into a table showing the total annualrainfall depth (mm) and the averagemonthly rainfall depth (mm) (Appendix E Average Annual Rainfall). We were then able to plot the total annual rainfall on a graph(Figure 3) to see if there were any long-term trends.

Annual Rainfall (1963 2007)

0

500

1000

1500

2000

2500

1963

1964

1965

1966

1967

1968

1969

1970

1971

1972

1973

1974

1975

1976

1977

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

Year

Rainfall(mm)

Total Annual Rainfall

Average Annual Rainfall

Standard Deviation

Figure 3 - Total Annual Rainfall

Figure 2 - NIWA Rain Station (Google Earth)


24/47


17

After examining the long-term trends of the graph it was found that the average annualrainfall for the region was relatively consistent over the 45-year period. As such we were ableto deduce that the Annual Average Rainfall Volume was 1,283 mm/year.

With this annual average rainfall volume we were then able to follow the North Shore City

Guidelines to calculate the recommended size of the tank:

The roof area had been identified by Liz Mars as111 m. This was calculated by multiplying thelength by the width of the collection area (Figure4) to give the total catchment area for our study.

Using (1), we were able to calculate the totalexpected amount of rainfall that would be captured by our rainwater harvesting system.

ageAnnualAverRoof VAV = 8.0 (1)

daylitresV

yearmV

yearmmmV

/312

/114

/12831118.0

3

2

=

=

=

Current literature states that only 80% of rainfall is actually captured and the rain tanks are

sized to provide approximately 10 days storage volume for the daily expected averagevolume (North Shore City Council, 2008). This means that for our daily expected averagerainfall volume over the 45 year period of 312 litres/day (114 m/year) we should have a tankwith storage capacity of approximately 3,120 litres. The closest tank size to this is a 3,200litres tank and is produced by all the major tankcompanies.

There are no Factors of Safety in this calculation.However, as the Mars residence has two parts toits roof structure, a flat area and a sloped area(Figure 5), we intend to only use the flat area

(79.73 m) to keep the installation process tidy.Otherwise we would have a downpipe runninghorizontally across the end wall of the house,looking unsightly and as Liz has kindlyvolunteered her property for the study, we want tokeep it as tidy as possible. As a result our totalroof area is slightly smaller than what is designedfor, but in theory there is less chance of the tankoverflowing.

Liz Mars initially requested that we install a tank with a volume of 5,000 litres as she intends

to keep the system upon completion of the study, because she feels that Akaroa will facesummer water shortages in the not too distant future. As a result of this she offered to meetthe extra cost involved from having a 5,000 litre tank as opposed to a 3,000 litre tank.

Figure 4 - Area of Roof Catchment

(North Shore City Council)

Figure 5 - Mars Roof (Liz Mars)


25/47


18

However when we explained to her how the tank was sized, including that we only intendedto used the flat part of the roof, she was happy to have just a 3,200 litre rainwater tank asoriginally sized. Irrespective of this, we had hoped to get sponsored by the tank manufacturersand get either a free or subsidised tank. A sketch of the system can be seen be seen below(Figure 6)

6.3 Installation of Rainwater Harvesting System

The rainwater harvesting system was installed at the Mars Residence on Thursday 26 June2008, prior to the commencement of data collection on 1 July 2008. The installation wascarried out by us, in accordance with the manufacturers instructions (Appendix B RXPlastics Site Preparation and Tank Installation).

We hired a trailer for the day, at a cost of $40 for full-day hire, and drove to Mico Pipelines to

acquire the required fittings required for the installation of the rainwater harvesting system(Appendix F Mico Pipelines Invoice). The required fittings were:

A leaf slide, which was attached to the downpipe above the tank

2 x 90 80 mm uPVC bends, used for plumbing the tank to the downpipe

4 x 3 m length of 80 mm uPVC downpipe, for plumbing the tank to the house

3200 litre RXP foam water tank

2 x 90 25 mm LDPE bends, to connect the tank level indicator to the tank

1.2 m of 25 mm clear tubing, for the tank level indicator

6 m of 50 mm alkathene pipe, used as the overflow for the tank

2 x 90 50 mm LDPE bends, used as part of the overflow

20 mm polyethylene tank connector, for the tank outlet

20 mm BSP ball valve, for the outlet tap

20 mm sprinkler adaptor, to connect aconventional garden hose to the outlet

We then drove out to Ashburton to pick up the

3200 litre foam tank from RX Plasticsmanufacturing facility. The tank had been procuredfree of charge as it was a seconds tank, this wasdue to a bubble in the side-wall of the tank which isan aesthetic defect and has no effect onperformance. RX Plastics also kindly donated to usthe clear tubing and two 90 25 mm bends to beused as the tank level indicator.

Once the tank was loaded onto the trailer we droveout to Akaroa to install the system. The first part of the installation involved digging out the

site for the tank to sit on. The tank required a firm level base to provide adequate support. Thearea needed to be cleared of any vegetation and sharp objects to ensure the tank would not bepunctured in any way. As the tank was being situated on a hill it required a wedge to be cut

Figure 6 - Conceptual Outlay of System

(Waitakere City Council)


26/47


19

out of the hillside. The total volume of the wedge was approximately 1.5 m. Thisexcavated material was spread around the garden area aslandscape material, and used to create a clear path to the tankitself (Figure 7).

As there were two of us doing the installation we were ableto simultaneously dig the solid foundation for the tank, andprepare the tank and spouting for installation. This involveddrilling the required holes in the tank for the necessaryfittings. These included:

A 20 mm hole in the side of the tank for the outlet tap

Two 25 mm holes in the side of the tank for the tanklevel indicator

A 50 mm hole in the side of the tank for the overflow

pipe An 80 mm hole in the top of the tank for the inlet

To prepare the spouting for the rainwater harvesting systemwe had to cut away some of the existing 80 mm aluminiumdownpipe to connect the leaf slide (Figure 8). Once this wasin place we replaced the removed aluminium downpipe with80 mm uPVC downpipe of the same colour. This was done toblend in with the existing spouting, while negating any issuessurrounding connecting uPVC downpipe to the existingaluminium downpipe.

Once the solid foundation for the tank was prepared and theexcess soil sufficiently landscaped, we were able to roll thetank up the hill and put it in place. With the tank in place andlevel, it enabled us to install the fittings to the tank andplumb it up to the house. This involved connecting the cleartank level indicator up the side of the tank, installing the 20

mm outlet tap at the bottom the tank and attaching the 50 mmoverflow pipe to the side of the tank. In the event that the tank

should completely fill, the overflow from the tank was be piped back into the domestic

stormwater system. We then connected the 80 mm tank inlet to the 80 mm downpipe,completing the installation of the rainwaterharvesting system (Figure 9). Prices for therequired fittings are shown in Table 3.

As a part of the manufacturers installationinstructions we were required to partly fillthe tank. For this we filled it until watercame out the 20 mm outlet tap, resulting inapproximately 100 mm water in the bottomof the tank.

Figure 7 - Path to Tank

Figure 8 - Leaf Slide

Figure 9 - Rainwater Harvesting System


27/47


20

By pure coincidence the following day there was 56mm of rainfall at the site, which completely filledthe tank. As a result of this rainfall Liz noticed that

one of the fittings at the base of the tank was leaking(Figure 10). This required us going out to the site totighten the fitting and also enabled us to take photosof the system, as it was after dark when we hadpreviously finished installation.

6.4 Data Collection

6.4.1 Baseline MonitoringBaseline monitoring in this case can be defined as measuring and recording the currentpotable water consumption values for the Mars residence. This can be done by reading andrecording the flow meter installed at the property boundary (Figure 11) to give the currentdomestic supply consumption.

To achieve this, water use was recorded at the Mars residence for one month prior toinstalling the rainwater harvesting system. The property had a flow meter installed at theproperty boundary which was read and recorded daily by Liz Mars from 1 June to 30 June2008. Also throughout the month of June the daily rainfall was measured and recorded by LizMars, from her rain gauge. This allowed us to see if the rainfall captured was typical of themonth of June when compared to the 45-year average values for June.

At the time of the baseline monitoring period, Liz Mars washedher car about once a fortnight and watered her gardenapproximately once or twice a week. Throughout the study wecontinued to find out how often these two events occurred and ifshe was using rainwater to do them i.e. taking demand off the potable supply. We also assumed that the leaks within her pipeswere negligible, due to her house being relatively new, as

substantial pipe leakage would greatly affect our results.

Unfortunately, due to the adverse weather conditions experiencedthroughout our test period very little water was actually used fromthe system productively in place of potable water. Theimplications of this on our results are discussed fully in Section8.0 Discussion.

6.4.2 Results CollectionOnce the data collection period had commenced, 1 July 2008, daily water measurements were

taken by Liz Mars, to determine the quantity of water collected and used throughout the study.The measurements consisted of:

Figure 10 - Leaky Fitting (Liz Mars)

Figure 11 - Flow Meter


28/47


21

Recording the 24-hour rainfall depth from the rain gauge, to give us the total volumeof rainfall within each 24-hour period.

Recording the level within the tank from the tank level indicator. This gave us the totaldepth of water in the tank, from which we can calculate how much water has beenused from the tank.

Recording the flow meter at her property boundary. This told us her current potablewater consumption from which we can work out the reduction in demand.

The tank level and rain gauge measurements were recorded daily, and the flow meter weeklyand the data was emailed to us every Wednesday.

6.5 Data Analysis

Upon receiving the weekly collected data we carried out a detailed analysis of it. Thisinvolved examining trends and looking at how much water is used compared to how much iscollected. The data was used in conjunction with NIWA climate and rainfall (CliFlo) data forthe region to analyse the conditions accurately. The water quality tests were compared againstthe New Zealand Drinking Water Standards 2005 as well as government legislation (e.g. CCCguidelines, Resource Management Act 1991, Natural Resources Regional Plan). Thisprovided us with an indication of the appropriate end use of the harvested water.

6.6 Water Quality Test

Rainwater supply can be used for both potable and non-potable uses. However, this isdependent on the water quality. One of the project objectives is to assess the quality of thewater and the implications on the end use.

Rainwater quality can be affected by exposure to air pollution caused by large industrialaction such as, cement factories, gravel quarries or a high concentration of vehicle emissions.In this case, it was expected that the remote location should not be affected by air pollution.We expected the main source of contamination would occur after contact with the roofsurface and subsequent delivery and storage.

A sample of tank water was collected by us on 10 September 2008 from the tank outlet andsent away to Hill Laboratory for testing. Ideally, the sample would have been taken after along dry period followed by a heavy rainfall this is expected to give the worst case waterquality results. However due to time constraints we had to just take a sample of the tank waterduring normal working conditions. The water was tested for pH, turbidity, conductivity,hardness, solids and coliforms as recommended by (Matt et al., 2001). Stan Abbot has alsosuggested testing for E. Coli and Total Coliform count along with lead. These parameterswere compared to the Drinking Water Standards (Ministry of Health New Zealand, 2005) andprovided us with an indication of the suitable end use of the water.


29/47


22

7.0 RESULTS

7.1 Akaroa Rainfall

The first part of the analysis involved looking at what the current situation was in Akaroa.

This was done by downloading the NIWA CliFlo data for the Onuku weather station (Figure2) and carrying out a full analysis of it (Appendix E Average Annual Rainfall). This gave us45 years of data to work with, from 1963 to 2007, so we were able to get an accuraterepresentation of what was happening in terms of rainfall within Akaroa.

Figure 3 shows that while there have been dry years; the frequency of exceptionally wet yearsis decreasing. However, irrespective of this, when a line of best fit was applied to the graph itappeared to be linear and constant, with a slightly increasing trend. As a result of this, theaverage annual rainfall was plotted almost exactly over the line of best fit, and from this wewere able to determine that the 45 year, average annual rainfall value was 1283 mm/year.When comparing this to the average annual rainfall value for Christchurch of 655 mm/year, it

can be deduced that Akaroa receives almost twice as much rain as Christchurch.

For the next part of the analysis of the NIWA CliFlo data we looked at monthly rainfall trendsover the 45-year period from 1963 to 2007. This produced Figure 12. This graph was used toidentify how the rainfall volumes experienced during our sample year (2008/2009) comparewith the 45-year monthly average rainfall volumes.

Monthly Average Rainfall

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

Janu

ary

Febr

uray

Mar

chAp

rilM

ayJu

ne July

Augu

st

Sept

embe

r

Octobe

r

Nove

mbe

r

Dece

mbe

r

Month

Rainfall(mm)

Monthly Average Rainfall

Annual Average Monthly Rainfall

Standard Deviation

Figure 12 - Monthly Average Rainfall

It was also interesting to note from this graph that September is the fourth driest month of theyear, after the three summer months from December to February.


30/47


23

7.2 Rainwater Harvesting System

7.2.1 Baseline PeriodPrior to the rainwater harvesting system being installed, we carried out a baseline monitoring

period to determine the current consumption of potable water at the Mars residence. Thisinvolved Liz Mars reading and recording the values of the flow meter at her property boundary from 1 June to 30 June 2008. Also, throughout this period, the daily rainfall wasmeasured and recorded by Liz Mars, from her rain gauge. This allowed us to see if the rainfallcaptured was typical of the month of June when compared to the 45-year average values forJune.

Daily Water Use (June)

0

500

1000

1500

2000

2500

3000

3500

1Ju

n08

2Ju

n08

3Ju

n08

4Ju

n08

5Ju

n08

6Ju

n08

7Ju

n08

8Ju

n08

9Ju

n08

10Ju

n08

11Ju

n08

12Ju

n08

13Ju

n08

14Ju

n08

15Ju

n08

16Ju

n08

17Ju

n08

18Ju

n08

19Ju

n08

20Ju

n08

21Ju

n08

22Ju

n08

23Ju

n08

24Ju

n08

25Ju

n08

26Ju

n08

27Ju

n08

28Ju

n08

29Ju

n08

30Ju

n08

Date

WaterUsed(litres)

Daily Water Use

Average Monthly Water Use

Figure 13 - Daily Water Use (June)

The total volume of potable water used throughout the month of June was 12,410 litres.Figure 13 shows that the daily volumes of water used throughout the baseline monitoringperiod vary greatly. Some explanations for the variances within the graph are as follows:

The period of no data from 4 to 7 June Liz was away so no water was used during thisperiod

The spikes on 3 and 15 June Liz used both the washing machine and dishwasher onthe same day

The extreme value on the 21 June (3,002 litres) Liz watered the Coprosma acerosa,then had visitors arrive so the garden irrigation was left on throughout this period

The period from 26 to 30 June Liz had a guest staying and washing machine use washigh

From this baseline data it can be determined that the average daily water use throughout thisperiod was 414 litres/day.


31/47


24

7.2.2 RainfallThroughout the data collection period (1 July to 30September) Liz Mars was measuring the 24-hour rainfallvolume from the rain gauge (Figure 14), to give us the total

volume of rainfall within each 24-hour period. These valueswere compared against the CliFlo 45 year average valuesfor the same months to determine whether or not the rainfallvolumes experienced during our testing period weretypical rainfall volumes for Akaroa.

Figure 15 shows the monthly rainfall volumes as measuredfrom the rain gauge throughout our test period, comparedagainst the calculated CliFlo 45 year average rainfallvolumes for the same period.

Monthly Rainfall

0.00

50.00

100.00

150.00

200.00

250.00

300.00

350.00

July August September

Month

RainfallVolume(mm)

2008

45 Year Average

Standard Deviation

Figure 15 - Monthly Rainfall

From the graph it can be seen that the July rainfall value of 236.6 mm is well above the 45year average of 171.3 mm. The August rainfall value of 152.2 mm is very close to the 45 yearaverage value of 159.0 mm. The September rainfall value of 52.2 mm is low when comparedto the 45 year average value of 89.4 mm. Overall it can be determined that our test period Julyto September 2008, was during a wet winter (June to August) as there was an above averagerainfall volume. However, they are still within one standard deviation (68.2%) from the meanso can be classified as wet but not extreme weather conditions.

It is interesting to note at this point that within any 24 hour period, 38 mm of rainfall over the79.73 m catchment area is all that is required to completely fill the rainwater tank fromempty.

Figure 14 - Rain Gauge


32/47


25

As discussed earlier, the total area of the Mars roof is 111 m. However for the purpose of thestudy and in the interest of neatness we only utilised the flat surface area of the roof, whichwas calculated to be 79.73 m. Multiplying this roof area by the collected rainfall volume foreach month it was possible to determine the total potential volume of rainwater availableduring our July to September test period (Table 5).

Table 5 - Potential Rainfall Volume Available

Monthly VolumeAvailable (m

3)

June N/A

July 15.09

August 9.70

September 3.65

Total 28.44

From this table it can be seen that the total potential volume of rainwater that could have beencollected during out testing period was 28.44 m. However, the majority of this rainwatervolume would have flowed down the black alkathene tank overflow pipe, and into thedomestic storm water system, as the rainwater tank was full for the majority of this period.

7.2.3 Flow MeterAlso during the 1 July to 30 September data collection period Liz Mars was recording theflow meter readings from the flow meter at her property boundary. This was required toenable us to determine her potable water consumption throughout our test period, from whichwe were able to work out the reduction in potable water demand.

Monthly Potable Water Usage

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

June July August September

Month

VolumeUsed(litres)

Figure 16 - Monthly Potable Water Usage


33/47


26

Figure 16 displays the domestic potable water use at the Mars residence throughout the baseline and testing periods (1 June to 30 September). The June baseline value of 12,410litres was measured prior to the installation of the rainwater harvesting system, while the July,August and September values were recorded with the system in place.

It is interesting to note that both the July consumption value of 15,641 litres and the Augustconsumption value of 13,450 litres are both greater than the June baseline consumption value,while the September consumption value of 10,607 litres is lower. These discrepancies can partly be explained however, as Liz was away from 4 to 7 June i.e. during the baselinemonitoring period. Also, Liz had her son staying for a period of time during the month ofJuly, explaining the increase in consumption.

Another possible explanation for the discrepancies between the baseline consumption valueand the July to September consumption values is due to the generally adverse weatherconditions. The cold weather and continual rainfall throughout the winter months has meantthat there has been more than sufficient water on the gardens and Lizs windows, car and

kayak have either not required cleaning, or have not been able to be cleaned due to theweather. These are all activities that would typically be undertaken utilising the water fromthe rainwater harvesting system.

7.2.4 Rainwater Harvesting SystemThe final piece of data collected by Liz Mars during the 1 Julyto 30 September collection period was the recording of thewater level within the tank by measuring the height of water inthe tank level indicator (Figure 16). This gave us the totaldepth of water in the tank, from which we were able to

calculate the volume of water that had been used from thesystem.

After analysis of the values collected by Liz, and taking intoaccount the dimensions of the tank (1850 mm diameter, 1558mm high) and the height of the 50 mm alkathene overflowpipe (1120 mm), we were able to produce Table 6 and Figure18, below. As the tank was full for the majority of our study,Table 6 shows the volume of water that was emptied out of thetank or utilised for beneficial purposes.

Table 6 - Rainwater Volume Used

MonthVolume Used

(m3)

July 5.14

August 6.92

September 1.40

Total 13.46

Figure 17 - Clear Tank

Level Indicator


34/47


27

Rainwater Usage

5.14 m

6.92 m

1.40 m

July August September

Figure 18 - Rainwater Usage

This graph shows that during July, 5.14 m of rainwater was used from the system; duringAugust, 6.92 m of rainwater was used from the system; and during September, 1.40 m ofrainwater was used from the system. Unfortunately however, these values are not indicative ofactual consumption. This is because the majority of this water was used by Liz either to

ensure the system was working correctly, or just flushed down the domestic storm water pipeto provide variability in our readings and allow us to ensure our calculations and data analysiswere accurate.

Unfortunately, due to the adverse weather conditions, very little water was actually used fromthe system productively in place of potable water. This issue and the resulting consequencesare discussed fully in Section 8.0 Discussion.

It should also be noted that even though the capacity of the tank is 3,200 litres (3.2 m), due tothe location of the overflow pipe the maximum storage volume within the tank is 3.01 m.

7.3 Water Quality Testing

Testing was carried out under conditions to best provide indicative results of the waterquality. The worst case scenario described as a long dry period followed by a heavydownpour was not logistically possible within the time frame of the project. Samples weretaken from the outlet of the tank to best represent the actual water used. The outlet wasallowed to flow for about 3 minutes to flush the valve of any bacterial growth that may havegrown on the outlet and thus affected the results. At the time of sampling the tank was closeto full level.

The samples were placed in their respective bottles and kept under the recommendedtemperature of 10 degrees (Figure 19). This prevents the growth or decay of the micro-


35/47


28

organisms. The samples were then sent to Hills Laboratories to conduct the appropriatetesting (Appendix G Hill Laboratories Test Results).

The parameters that were perceived to create a problem include: pH, turbidity, conductivity,

hardness and alkalinity, Total Organic Carbon(TOC), E. Coli and Total Coliform, and metalconcentrations lead and aluminium. Sodiumand chloride are also tested to determine thesalt concentrations. Polyaromatic hydrocarbons(PAH) are tested to determine the effect fromthe vehicle traffic.

Sea salt spray may have some effect on thewater quality. Long periods of onshore windsand squally weather conditions without rainfall

may worsen the foreseen problem. Sodium, chloride and conductivity indicate the presence ofsalt.

E. Coli and Total Coliforms indicate the presence of disease causing microorganisms. Diseasecausing microorganisms are known as pathogens and include bacteria that cause choleraand typhoid-fever.

The presence of Total Organic Carbon (TOC) indicates the level of organic material enteringthe system. The main source of organic material is from overhanging trees and windblownleaves. Reducing the amount of TOC is essential to ensure that the system does not produceby products due to the build up of contaminants.

Polyaromatic hydrocarbons are evident in areas with high traffic flow. Ashpalt roofs can alsobe a source of PAHs, which are a health concern.

pH, turbidity, hardness and alkalinity all give an indication of the general quality of the water.New Zealand rainwater has a pH of about 5.7 which can be aggressive to metals. Turbiditywill give some indication of the suspended solids in the water.

The water quality tests show an overall positive result. Two determinands showed valuesoutside of the maximum acceptable values (MAV) outlines by the Ministry of Health. Totalcoliforms were unacceptable and the pH (6.3) was reasonable but outside of the recommended

range of 7 8.5. The results are shown in full compared against the Drinking Water StandardsNew Zealand in Table 7.

Figure 19 - Water Samples


36/47


29

Table 7 - Water Quality Test Results

Parameter Value MAV Units

Turbidity 0.87 2.5 NTU

Rainwater Harvesting - An Option to Reduce Demand on Water Supply

Documents

Transcript of Rainwater Harvesting - An Option to Reduce Demand on Water Supply