NAHRIM's Experiencein Rainwater Utilisation System Research-Slides[1]

8/2/2019 NAHRIM's Experiencein Rainwater Utilisation System Research-Slides[1]

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NAHRIMS EXPERIENCE IN

RAINWATER UTILISATION SYSTEMS RESEARCH

Ahmad Jamalluddin bin Shaabanand Huang Yuk Feng

National Hydraulic Research Institute of Malaysia (NAHRIM)

Water Resources Management Division

Lot 5733, Jalan Putra Permai, 43300 Seri Kembangan, Selangor

ABSTRACT

With the global change in weather patterns affecting rainfall distribution temporally and

spatially, rainwater harvesting and utilization has certainly be given an added dimension and approach

towards an integrated environment friendly and sustainable urban water resources developmentinitiative. With the advantage of the countrys blessed generous rainwater resources, capturing it for

present and future use on-site would undoubtedly help to supplement city public water supply and

possibly replacing the non-potable common whilst also reducing the potential of urban flash floods via

reduction of peak storm runoff. Consequently, NAHRIM has carried out three main pilot projects forrainwater harvesting, which include (i) a double storey terrace house located at Taman Wangsa

Melawati, Kuala Lumpur, (ii) a mosque complex at Taman Bukit Indah, Ampang, and (iii) theHeadquarters of the Department of Irrigation and Drainage (DID) in Kuala Lumpur, in collaboration

with DID. Harvested rainwater of the projects is used for non-potable purposes only. This paper is

aimed at discussing the R&D on rainwater systems carried out by NAHRIM with focus on systemdesign, installation cost and unit cost, deployed for the double storey terrace house at Taman Wangsa

Melawati and the mosque complex at Taman Bukit Indah. The amount of rainwater use and its

reliability from the NAHRIM in-house studies are explained. The various benefits of rainwater, issues,

strategies and future plans for rainwater harvesting and utilisation are also presented.

1.0 INTRODUCTION

Rainwater harvesting and utilization has been practiced in Malaysia especially in the villages since

long ago. Subsequent to the 1998 April drought, the Minister of Housing and Local Government on 7May 1998 has expressed the Governments interest for houses to be designed to include facilities for

collecting rainwater. In 1999, the Ministry of Housing and Local Government has produced a

Guideline on Installing a Rainwater Collection and Utilization System (Rainwater Guideline, 1999).This guideline is intended as an ideas manual for reference for those who want to install a rainwater

harvesting and utilization system. It aims to encourage the owners to think and adopt wherever

possible appropriate innovative alternatives which offer real advantages and adaptable to their needs.

In support of the Government's interest in rainwater harvesting, NAHRIM through its

collaboration with other government agencies such as the Department of Irrigation and Drainage(DID), the Department of Local Government (JKT), Universiti Teknologi Malaysia (UTM), Universiti

Sains Malaysia (USM), Universiti Putra Malaysia (UPM) and Universiti Malaya (UM), has been

pursuing R&D on rainwater harvesting with focus on system design and installation cost, systemperformance and system operating and maintenance cost, unit cost, effectiveness in reducing the urban

flash flood problems, and policies, by-laws and proposing incentives for system implementation.


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2.0 RAINWATER HARVESTING SYSTEM AT A DOUBLE STOREY TERRACE HOUSE

The rooftop has cement tiles and has a roof area of 60 m2. The rainwater is conveyed from the rooftop

to the storage tanks via a series of gutters and pipes. Rainwater from the rooftop is usually

contaminated with dirt, bird droppings, leaves, etc. The first flush of rainwater from the roof surface is

directed into the first flush tank of 200 litres to filter out these materials from the rainwater before it is

stored in the ground floor storage tanks.

For the 1st

phase of the study, two black High Density Polyethylene (HDPE) tanks with a 2500liter capacity each were installed as storage tanks. The water use and quality are monitored over one

year. In the 2nd

phase, these two black HDPE tanks are replaced with a better storage tank design

taking into consideration the aesthetic and utility aspects. It is a brick storage tank of 5000 litrescapacity and the space above the tank is used as a childrens play area and also for drying clothes (See

Figures 1a, 1b and 1c). 3300 litres of storage is allocated for rainwater reuse (bottom portion), while

1700 litres is for detention storage (top portion). A 1.0 horsepower electric pump with minimum headof 12 m was installed to pump water from the ground storage tank to the roof rainwater tank. This tank

was installed on the roof in addition to the existing potable water roof tank that is a mandatory

requirement. The additional tank has a separate rainwater supply for non-potable household use. Thestudy house also has a separate plumbing system to cater for the rainwater usage. Since rainwater was

to be used for non-potable use, the plumbing system was installed in such a way that there was a

bypass connection for each flushing cistern. In case of water shortage or non-availability of rainwater,

the public water supply can be switched on. The rainwater plumbing system was also connected to thewashing machine pipe and pipe for general cleaning.

2.1 USE AND RELIABILITY OF RAINWATER

The occupants of the house under study include two adults and four school going children. The house

has three bathrooms. The amount of rainwater used for facilities was monitored with mechanical watermeters in each facility. Readings are taken and recorded manually. The water use figures obtained are

comparable with water use figures from literatures and specifications of the respective products. Table

1 shows average water use for facilities using rainwater based on twelve months data. Since there wasno treatment to the rainwater collected, it is strictly used for toilet flushing, general washing and

washing clothes.

Table 1: Rainwater Use for Various Facilities

ItemAveragedaily use(liters)

AverageMonthly use

(liters)%

Washing clothes 300 9,000 66

Toilet Flushing(3 W.Cs)

90 2,700 20

General Cleaning(including car andmotorcycle washing)

65 1,950 14

TOTAL 455 13,650 100

(Source: Shaaban and Appan, 2003)

Monthly Rainwater use = 13,650 liters

Monthly water use (from public water supply) = 27,000 litersTotal Monthly Household Water Use = 40,650 liters


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From the above, household use for non-potable purpose using rainwater contributes 34% of the total

monthly household water use.

A simulation model was developed and used to check on the reliability of the rainwater harvesting

system based on the 5 m3

storage tanks and water demand of 455 liters/day. The model was run using

15 years of daily rainfall data from DID Ampang. The rainfall characteristics are tabulated below:

Table 2: Rainwater Use for Various FacilitiesThe average annual rainfall 2,542 mm

The highest daily rainfall 166 mm

The longest period without rain 29 days

Average period without rain 15 days


The parameters specified for the simulation model were as follows:Size of roof = 60 m

2.

Run-off coefficient = 0.80

First Flush = 1 mm of rainfall or approximate 60 litres.

No. of persons = 6Average usage per person per day = 75.8 litres.

Total water usage per day = 455 litres

Simulating with these parameters, the reliability of the system was found to be 66.2% for a

water use of 455 litres/day and storage of 5 m3. To attain 74% reliability the storage need to be

increased 8 times i.e. up to 40 m3. With the limited roof area, a big increase in storage would result in

only a small increment in reliability. One possibility of further increasing the system reliability is to

increase the roof area (using the other half of the house roof estimated at another 60 m2) so as to catch

more rainfall and thereby increase the yield. This necessitates installation of extra gutters, piping,storage tanks and a pump.

2.2 ECONOMIC ASPECTS SYSTEM COST AND UNIT COST

From a project cost evaluation by NAHRIM, the system cost and unit cost for the rainwater cum

detention storage system (brick tank) for a double storey linked house (Taman Wangsa Melawati,Kuala Lumpur) is as follows:

Table 3: System Cost for the Rainwater Cum

Detention Storage System - Brick TankComponents Amount (RM)

Gutter (uPVC) 150.00Conveyance System 200.00

Plumbing works 400.00Water tank (top) 200.00Brick tank (ground) 5000 liters capacity 2,600.00Water pump (electrical) 750.00

TOTAL 4,300.00



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In working out the unit cost of water for the system, the life expectancy of the system is taken as 25

years. The operating cost includes O&M of the pumps and electricity. The unit cost of water was thenworked out to be RM 2.63/ m

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The current water tariff for domestic households (Kuala Lumpur and Selangor) is RM 2.00 for water

consumption above 35 m3

per household per month. However, there seems to be an imminent increasein the near future. It can be seen that the unit cost of rainwater cum detention storage system at RM

2.63/m3 is 1.3 times much higher than that of piped water. As practiced in Japan and elsewhere, the

Government may need to provide subsidies to encourage the public to install rainwater cum detentionstorage systems.

3.0 RAINWATER HARVESTING SYSTEM AT A MOSQUE COMPLEX

The rainwater collected is stored in the storage tank (underground) and pumped to the toilets and

standpipes. The system component consists of a catchment subsystem, filtering cum conveyance

system, storage subsystem, pumps, and internal plumbing. The schematic arrangement of the systemand the site plan of the mosque are shown in Figures 2 and 4, respectively.

Catchments Subsystem

For this rainwater harvesting system, part of the rooftop and also a portion of the mosque compound is

the catchments subsystem. For non-potable use, any roofing material can be used as the catchmentssubsystem. The roof material used in the study is of metal tiles. The roof area of the mosque utilised

is 644 m2

and the mosque compound area utilised is 2925 m2.

Conveyance System

The function of this subsystem is to convey the rainwater roof runoff and the filter the storm runoff

from the catchments sub-system to the underground storage tank. Basically this subsystem consists of

3 main components. These components are the gutter, downspouts and the conveyance pipes (filterstrips covered with geotextile called hydronet) placed in the concrete drains. Rainwater from the

rooftop is channeled to the gutters and then through the downspouts and finally through theconveyance pipes to the storage tank. While the storm runoff is channeled to the filtering cum

conveyance pipes to the storage tank. The gutters were incorporated in the design. It is concealed and

and formed as part of the pillar of the mosque. There were several downpipes provided to cater for therainwater. At the downspout inlet a net is placed. The net is to trap rubbish, leaves and other debris

usually found on rooftops.

Underground Storage Tank

The collected rainwater is stored in the underground storage tank (Figure 3) via the conveyance pipeafter the filtration by the filter strips. The storage tank is constructed using polyethylene moduleswrapped in geotextile called hydronet and an impermeable HDPE liner. The underground storage tank

could withstand loads of up to 40 KN/ m2, as above it is the mosque car park. An overflow pipe is

provided to cater for storm inflow of 10 year return period.


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Submersible Pumps

Two submersible pumps (2HP), one to be operational and the other one as a back-up (variable speed

motor to ensure immediate response to the demand flowrate) are used to pump rainwater from the

underground storage tank to the toilets and stand pipes for general cleaning and gardening purposes.

The submersible pump was chosen since it does not pose any suction problems (one of its advantage).

A pressure vessel (pressure set at 8 bar) is placed after the submersible pump to maintain constantpressure (1 bar) at the outlet.

Backup Water from Water Supply Department (WSD)

In case the rainwater in the storage tank is insufficient during dry periods, supply from WSD would befed automatically to the rainwater storage tank. This would ensure uninterrupted water supply to the

system. Similarly, if there is a blackout and electricity is not available for the pumps to operate then

the public water supply would come on automatically to the toilets.

Plumbing System

The plumbing system is independent from the public water supply as per requirements of WSD. For

potable use (cooking and drinking), water supply must be direct from WSD. As practiced in overseas

country, color coding is used on the plumbing system to distinguish between municipal water supply

and supply from rainwater. Signage were also provided at the toilets and standpipes to inform thatrainwater is used and reminding the public that the rainwater is not meant for drinking purposes.

3.1 PROBLEMS ENCOUNTERED DURING AND AFTER CONSTRUCTION

Initially the conveyance pipe is intended to channel the roof runoff only but as this is a retrofitting job

and the mosque committee stipulates no hacking of the concrete perimeter drains, the use of filterstrips wrapped with hydronet was adopted to serve as the filter cum conveyance pipe. Additional

storm runoff from the mosque compound is also channelled into the filter cum conveyance pipes.

Incorporating the storm runoff from the mosque compound has its disadvantages. During

heavy rainstorms there could be overflow of sewage from the toilets that could pollute the storm

runoff.

3.2 USE AND RELIABILITY OF RAINWATER

The peak daily water demand is estimated at 15,000 litres based on 2,500 persons utilizing 6 litres pertoilet flush. The total peak daily water demand of the mosque for wudhu, toilet flushing and general

cleaning is estimated at 26,250 litres.

Utilizing 15 years of rainfall data from Department of Irrigation and Drainage (DID) Ampang

and inputting the daily water demand, catchment area and appropriate runoff coefficient to a simple

simulation model, the reliability (where Reliability = Delivered volume of rainwater / DemandVolume) of the system was found to be 60 %.


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3.3 ECONOMIC ASPECTS SYSTEM COST AND UNIT COST

System cost includes supply and installation and varied accordingly depending to the type of materials

used. Since the gutters were already incorporated in the design of the mosque, the additional costs for

rainwater utilization were the costs of underground storage tank, conveyance pipes, pumps with sensor

and additional plumbing separated from the WSD water supply system. A breakdown of the cost of

the various components of the system in Malaysian Ringgit (RM) is presented in Table 5.

Table 5: Cost of System Components_____________________________________________

Conveyance System to cater for stormwater (modification) RM 15,000

Plumbing works RM 5,000Underground Water Tank (60 m

3capacity) RM 60,000

Water pumps including sensor RM 15,000

TOTAL RM 95,000

___________________________________________________________________________

In working out the unit cost of water for the system, the life expectancy of the system is taken as 25years. The operating cost includes O&M of the pumps and electricity. The unit cost of water was then

worked out to be RM 1.26/ m3.

3.4 MAINTENANCE OF THE SYSTEM

Maintenance of rainwater equipment is necessary to ensure that clean rainwater is collected and used.

Pertinent aspects of maintenance involved are as follows:i) Catchment area clean regularly leaves, trash and animal excreta in catchment areas including

roofs.

ii) Filter cum conveyance pipes need to be checked periodically and replace damaged hydronetas required.

iii) Rainwater storage tanks Internal inspection carried out twice a year. The inside cleaned asrequired.

iv) Rainwater supply equipment Mechanical devices such as pumps are checked at least everythree months. Other devices should be checked every six months and maintained the same way

as public water supply equipment.

4.0 BENEFITS OF RAINWATER HARVESTING

The benefits of rainwater harvesting system to the country are many and can be broadly grouped intothe following:

(i) Rainwater utilisation for non-potable use can reduce the dependence and demand of publicwater supply;

(ii) The water saving would result in reduction of the water bill. With increases in water tariffthe future monetary savings from the Rainwater Harvesting System (SPAH) would be even

more attractive;(iii) According to the research carried out by NAHRIM on the SPAH pilot project for a double

storey terrace house located at Taman Wangsa Melawati (Shaaban and Appan, 2003),

SPAH is able to save up to 34% of public water use, in addition to the 10% of reduction inpeak discharge by assuming every terrace house has been installed with the same SPAH

(covers 19% of total catchment area). Further reduction of peak discharge, up to 50%, could


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be achieved by installing rainwater cum detention storage systems in the shophouses,

multipurpose hall, mosque, kindergarden and park, in this housing area. Reduction of peakdischarge not only reduces the needs of drainage system upgrading but also reduces the

impacts of flash floods and erosion. Erosion and flooding due to runoff from impervious

areas such as pavement and roofs will be reduced by rainwater harvesting as some rain is

instead captured and stored.

5.0 ISSUES IN IMPLEMENTING SPAH

The issues in implementing the rainwater harvesting systems in the country include:

(i) The lack of understanding of the public about the concept of rainwater utilisation;(ii) Aspects of design for locating rainwater equipment (example: downpipes, tanks and pumps)

not given consideration with respect to aesthetics of the environment, space savings and

ease of maintenance;

(iii) In the view of health aspects, breeding of mosquitoes can occur in pools of stagnant waterin gutters and also the rainwater tank (need to ensure gutters have adequate slope and

cleaned when necessary and prevent entry of mosquitoes into rainwater tanks and

introducing Abate or similar chemicals to kill mosquito larvae)

6.0 CONCLUSIONS

From the study on the double storey terrace house, the rainwater systems could meet up to 34% of thedomestic non-potable household water requirements at 65.5% reliability (for storage of 5000 litres) and

61.4% reliability (for a storage of 3300 litres) respectively. The unit cost of rainwater (with detention

storage) at RM 2.63/m3

is more costly compared with the piped water cost at RM 2.00/m3

for waterconsumption above 35 m

3per household per month.

10% reduction in peak storm runoff is achieved when rainwater cum detention storage systemsare installed at all the houses. Further reduction, up to 50%, in peak storm runoff could be possible

when the rainwater cum detention storage systems are extended to the shophouses, mosque,

kindergarten and parks/lawns in the housing area. Furthermore, the rainwater cum detention storagesystems for the park could be used for plant watering, firefighting and emergency use for the

community during a prolonged drought.

Based on the study on a mosque complex, it is possible to use rainwater for toilet flushing (with

60% reliability) which at the same time could save up to 34% of the public water supply annually. The

unit cost of rainwater at RM 1.26 per m3

is considerably higher compared to the water rate for religious

institutions (which is given special low tariff by the government). Nevertheless, such rainwatersystems when applied extensively to public and private buildings will reduce significantly the

dependence on public water supply thus contributing towards sustainable water resources development

especially in the rapidly growing urban areas of Malaysia.

Rainwater harvesting and utilisation especially in urban areas is likely to increase in future due

to its multifarious benefits such as reducing pressure on existing water supply systems and reduction ofurban floods. With its domestic and environmental benefits, rainwater harvesting systems could

become a standard feature of future homes and buildings supplementing the water needs of its

occupants. Issues arising from the implementation of SPAH should be handled with great care. Theeconomic benefits in terms of reducing the costs of urban flood mitigation works and downstream

damage reduction needs further investigation.


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8. REFERENCES

Rainwater Guidelines, 1999. Guidelines for Installing a Rainwater Collection and Utilisation System,

Ministry of Housing and Local Government, Malaysia.

Shaaban, A. J. and A., Appan, 2003. Utilising Rainwater for Non-potable Domestic Uses and

Reducing Peak Urban Runoff in Malaysia, International Rainwater Cistern Systems Conference,Mexico


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Figure 1a: Front View of Rainwater Harvesting cum Detention Storage System.

Figure 1b: View of Rainwater Harvesting cum Detention Storage System from the front of the house.


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Figure 1c: Various components of the Rainwater cum Detention Storage System

Gutter and down pipe from

roof

First flush tank

Rainwater cum detention storage tank

View of the Rainwater System

from the front of the house

Gutter leading to first

flush tank

1 HP electric pumpRainwater connection for

washing machine

Rainwater connection

for toilet flushing


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Figure2:SchematicA

rrangementoftheRainwater

System

Figure2:SchematicA

rrangementoftheRainwater

System


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Figure3:Underground

StorageTank(Cross-section)

Figure3:Underground

StorageTank(Cross-section)


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Figure4:SitePlanoftheMos

que

NAHRIM's Experiencein Rainwater Utilisation System Research-Slides[1]

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