Rain Water Harvesting Comparison Between Existing Techniques and Its Modification_Mohammad Ali

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Rainwater Harvesting: Comparison Between Existing Techniques And Its Modification

Hasan Mahmud, Mohammad Ali, Noor Ahmed 1

Dr. Jahir Bin Alam 2

1 Undergraduate Student, Department of Civil & Environmental Engineering 2 Assistant Professor, Department of Civil & Environmental Engineering

Shahjalal University of Science & Technology, Sylhet Fax : 880-821-715257, Email: [email protected]

Abstract: Gathering rainwater by using roofs, reservoirs and other collectors is called rainwater harvesting. The rainwater harvesting is considered as a possible answer to the global water use problem, especially where surface and groundwater is limited. Also rainwater is soft water, pollution free, iron & Arsenic free. The rooftop rainwater harvesting system seems suitable for Bangladesh, as the system will be designed only to supply drinking and cooking water. Catchments area in urban and rural area is totally depended on type of roofing material and size of area. Various parts of rainwater harvesting system gutters, downspouts, storage tank make easy to collect and preserve rain water. In Bangladesh they’re also some low cost different types of storage tank. In this present world there are different type of storage tanks available according to its construction and cost it makes vary in lifetime, size, quality of water. For a modified system, in the treatment process there is two steps. Screening out impurities large in size, first flush systems, sedimentation is in primary stage. Before storage (filtration) and after storage (disinfections) are in secondary treatment. It also needs some operation and monitoring. It can be routine wise on storage operation. Water quality monitoring on daily (e.g. turbidity, color) and weekly monitoring include disinfection, insect vector monitoring e.g. dengue. According to this demand the water budget is made. Low cost construction procedure has been discussed considering cost, code and safety issues. It can be supply not only in rainy season but also it can supply water for drinking and cooking by filtering and also by some treatment process by using pond or river water. Considering best system component for to design it. The system design is not so critical and it can be constricted easily. It initial cost is not so high because it is designed community base by the establish network rainwater collection system from near by houses. In this paper an attempt has been taken to find out and comparison between existing techniques and its modification.


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Introduction Gathering of rain water by using roofs, reservoirs and other collectors is called rain water harvesting. It is not a modern concept. In ancient Egypt and Rome, rain water was harvested by reservoir and canal, and was used for domestic purposes, cultivation, irrigation and in primitive small industries. For centuries throughout the world, people have still relied on rainwater harvesting to supply water for household, landscape, livestock, and agricultural uses. Before large, centralized water supply systems were developed, rainwater was collected from a variety of surfaces—most commonly roofs—and stored on site in tanks known as cisterns. With the advent of large, reliable community treatment and distribution systems and more affordable well drilling equipment, rain harvesting systems have been all but forgotten, even though they offer a source of pure, soft, low sodium water. A renewed interest in this time-honored approach has emerged due to:

• the escalating environmental and economic costs of providing water by centralized water systems or by well drilling;

• health concerns regarding the source and treatment of polluted waters; • a perception that there is cost efficiencies associated with reliance on rainwater.

Bangladesh is one of the smallest countries of the world having a total area of 143,000 square kilometer. Around 130 million people live in this deltaic plain land. Though it is a small country, but the social and culture practices, and the behavior and beliefs of the people vary in different parts across the country. Considering the geological formation and prevailing geo-hydrological situation of the country, the entire country can be divided into four distinct geo-hydrological areas, which are:

•Shallow Water Table Area •Low Water Table Area •Coastal Area • Hilly Area.

Each geo-hydrological area can again be divided into two parts in light of the country's arsenic situation, which are: •Arsenic-contaminated area •Arsenic-free area.

Safe Water and Sanitation is a prerequisite for sustainable public health development. In this regard Bangladesh had achieved a great success in ensuring safe water supply services to its rural population through providing hand tubewells that extract groundwater. This tubewell water was considered as the main source of safe drinking water in the rural area, but the detection of arsenic in 1993 in the groundwater of Bangladesh imposed a serious threat to this prime source of safe drinking water. Excessive withdrawal of groundwater through tubewell for irrigation is identified as one of the reasons for this arsenic contamination. More than 60% tubewells are now under the threat of arsenic contamination. Out of 64 districts of Bangladesh, 59 districts have found to be arsenic affected, which has risen an urgent need to develop alternative options for ensuring safe water to cope this disastrous situation.

Since ancient times rainwater harvesting was in practice to varying degrees throughout Bangladesh. With the proliferation of tubewells the practice has waned. Yet in the coastal areas and Hill Tracts some people still practice rainwater harvesting and use large earthenware pots (motkas) for storage. The detection of arsenic in groundwater in Bangladesh in 1993 has renewed an interest in alternative sources of drinking water. The heavy monsoon rains make rainwater harvesting a viable option for drinking water in Bangladesh. The common people's experience may not be adequate and systematic to suit a preconceived notion of a system, but people do know that their forefathers, albeit in a limited way, did rely on rains during heavy showers. Many countries in the region such as Sri Lanka, Thailand and Nepal have proven systems of rainwater harvesting. Efforts to promote rainwater harvesting should build on these experiences gradually improving tank design, fittings and costing to suit socio-economic environment in Bangladesh. Demonstration and promotion of rainwater harvesting systems that build on common and existing experiences is likely to meet general acceptance. The focus has been given on the household systems and the storage of rainwater to meet the total needs in the dry season may not be realistic, but the rainwater harvesting will be in combination with other water supply options in the project area. It may be rainwater harvesting in the monsoons and distant safe water tube well, BTU (Bucket Treatment Unit), SODIS, etc. in the dry seasons.

Qualitative Advantages I. Purest than any other sources:- Rainwater is one of the purest sources of water available. Indeed, the quality of Rainwater is an overriding incentive for people to choose rainwater as their primary water source.


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II. More qualified and free from pollutants:- Rainwater quality almost always exceeds that of ground or surface waters: it does not come into contact with soil and rocks where it dissolves salts and minerals, and it is not subject to many of the pollutants that often are discharged into surface waters such as rivers, and which can contaminate groundwater. III. Rainwater is soft:- Rainwater is soft and can significantly reduce the quantity of detergents and soaps needed for cleaning, as compared to typical municipal tap water. Additionally, soap scum and hardness deposits disappear, and the need for a water softener, often an expensive requirement for well water systems, is eliminated. Water heaters and pipes will be free of deposits caused by hard water and should last longer. IV. Attractive sources for pure water required for industries:- Rainwater’s purity also makes it an attractive water source for certain industries for which pure water is a requirement. Thus, industries such as computer microchip manufacturing and photographic processing may also wish to examine this source of water. V. Easy and low-cost collection system:- In Bangladesh rain occurs all over the year with low or high intensity with a higher intensity in rainy season. So rainwater is mostly available all over the year and it can be collected with very simple, easy and available equipment that concerns low-cost collection system. VI. It is really economical:- First of all rainwater is available and its collection is more easy and less expensive than any other source and system of water supply. On the other hand is merely free from pollutants and also from TDS, DS, SS although it may be contaminated by a very few amount of micro-organisms or pathogens during flowing over the collecting gauge. As a result in rainwater harvesting and using as potable or household purposes, no high efficient treatment plant is required whereas it the high requirement of any other water supply system. So rainwater harvesting is very much cost effective and it is more suitable than any other system for a poorer country like Bangladesh.

Social Aspect and Water Use • The monitoring findings show that the community people have socially accepted the rainwater and are

regularly using water for drinking and cooking purposes. • The user families also accept the plants' shape and architecture and feel proud of being the plant owner. • The women of the community are found very much interested on the RWHS, as because they were

involved in the construction process from the beginning to the end. Another cause is that they are getting safe water around their homestead and beside the kitchen, which save both time and labour that they used to spend for water collection.

• As the RWHSs have been constructed around the house premises, the women are able to maintain their religious and social restrictions.

• Due to the bitter taste, the users especially the children did not like to drink rainwater at the initial stage. But day-by-day, all the users (men, women and children) are getting habituated in using the stored water for drinking and cooking purposes.

• The RWHS is increasingly getting much popularity among the community people of the project area, and they opine that it is the easiest way of collecting water that can be used and safe both for drinking and cooking It also saves time and labour cost in comparison to other options, they added.

• The users opined that RWHS is better for drinking and cooking than the tubewell water. • From the users point of view the water consumption rate of 45 litre/day/family is sufficient for them. No water born disease was reported occurred within the community after the user groups started using the stored rainwater. Design of Rain Water Harvesting System The design of Rain Water Harvesting Systems was the important task during the initial stage of the project. During designing main emphasis has been given on different aspects in order that it can provide a suitable, affordable, safe, socially acceptable and sustainable alternative source of water for drinking and cooking purposes covering 8 to 10 months of a year. The design has been selected following the available regional (Nepali, Thai and Sri Lanka) models of storage tanks having the capacity of storing 500 L, 1.0 m³ and 2.5 m³, and made of different materials like concrete rings, brick, ferro-cement, etc. Before designing different models of RWHSs, the criteria for designing have been set based on the objectives and concept of the action research project and the information accumulated through the baseline survey conducted in the intervention villages. The major design considerations were the rainfall pattern of the project area (30 years rainfall data collected from the Water Development Board of the Government of Bangladesh), family size (nuclear family), water consumption per capita per day, suitable roof size and roof


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material, socio-economic status, design cost of the plants and availability of construction materials etc. The following parts of the Rain Water Harvesting System has been designed: i. Tank ii. Catchment iii. Gutter iv. Flushing System v. Collection Point A general types of RWHSs designed are described as follows: Storage Tank: The main variables for designing different models of RWHS are as follows: → Sizes of storage tank (500L, 1.0m3 and 2.5 m3) → Construction material (concrete rings, brick, ferro-cement, burnt clay, motka, etc.) → Different proportion of mortar → Thickness of storage reservoir The catchment, gutter, first flush and water collection point are the integral parts of a RWHS and therefore these components have been designed for easy O&M, better performance of the system and water use. In order make the RWHS popular; attempts have been taken to introduce some do-it yourself model such as motka for storage and polyethylene for collection. Catchment: Catchment is an important part in roof water collection. The quality and quantity of the collected water depend on the availability of suitable catchment. C.I sheet roof, polyethylene sheet over thatched roof, tiles roof, etc. are used as catchment. In some cases, the CI shade is used as catchment where any suitable catchment is not available. Gutter system: Gutter system is used as the means of transport of water from the catchment to the tank through an inlet pipe. Two types of gutter systems have been designed viz. GI sheet made and 3" dia PVC pipe. Flushing system: Flushing system is an important device to divert the first foul rainwater from entering into the reservoir. This device has been designed consisting of 38mm dia PVC pipe along with GI elbow and cap. All the joints of the pipes are joined with solvent cement. Collection point: Collection point has been designed to use maximum of water stored in the tank, to make the water collection process easy and also for hygienic purposes. The collection point is placed only 1" above the surface of the tank bottom, so that water can be collected using a tap. These collection points are usually made with different materials and have different shapes like brick-made circular or rectangular, earth-made pot, etc. The covers made of RCC and GI sheets are usually placed over the collection point for hygienic purposes. Modified Combine Water Supply System This is the system in which we can basically we can collect rainwater in wet season and in dry season we can get water by treatment surface water by treating them e.g. filtering and chemical treatment. Objective: 1. Assessment of the technical requirements for efficient rainwater harvesting, and test and improve on existing models and consider the role of private sector and the householder in establishing the facility; 2. Demonstration, testing and promotion of rainwater harvesting systems in WPP areas that have arsenic in groundwater through participatory strategies; 3. Introduce and test do-it-yourself models for the very poor; 4. Monitoring and documentation of construction, and performance of the rainwater harvesting systems in terms of user acceptance and user friendliness, water quality, water security and general system management; and 5. Development of construction manuals and procedures for the implementation of rainwater harvesting systems as an option in rural water supply. Construction of RWHS: To meet up the demand came out from the community people, it can be constructed have the storage capacity of 2.5 m3, 1.0 m3, 500 litre and 600 litre. Different types of construction materials can be used such as like RCC ring, ferro cement technology, bricks, etc. Mainly it is preferred circular/ rectangular brick tank, RCC. In this tank there are three chambers. The first one is initial storage tank which size is bigger than the other two. The second chamber is filter media which consist of different types of filter media to treat the surface water which is small in size. The third one is final storage chamber. A downward slop is provided from third chamber to first chamber.


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Water Treatment: For the rain water there is no need to treat for short time preservation. Only first flush system is provided to avoid the impure water which content air pollutants for first 10 or 15 minutes. This system also include screening, the functioning of special devices which removes various types of substances like debris, bird droppings, leaf- both fresh & degraded, worms, snails etc which will detoured water quality & also interfere with various components of treatment system. For the surface water it is treated by filter media and chemicals to remove the impurities. i. First Chamber: It is mainly used for sedimentation process for the surface water. This is the process causing the organic & inorganic particles heavier than water to settle by retaining water in the first chamber. These particles held in suspension in natural water mainly by turbulence and current & when the current is retarded, the suspended particles settle at the bottom of the chamber. This coagulation process is done by using a low cost available chemical Al 2O3.

ii. Second Chamber: It is small filter chamber. Treated wood charcoal will be used for bacterial removal. iii. Third Chamber: In this chamber both rain and surface water is disinfect by Ca(OCl)Ca. When rain water is preserved for long time in the tank to disinfect the growing accumulation of micro-organism is done by maintaining routine as defined. Water quality: Drinking water quality is desired well from the outlet of chambers on the basis of the experiment done in the laboratory. Routine Operation and Monitoring: A perfectly routined monitoring system should be developed for the assurance of batter quality of water, which mainly depends on local conditions like surrounding environment (trees, vegetations, air pollution etc). Monitoring and operation includes:-

A. Storage Operation. B. Water Quality Monitoring.

C. Insect vector Monitoring:

A. Storage Operation: • Clean the base or platform .Do not allow water logging around the unit. • Inspect the tap, joints, pipes, fittings, covers, gutter etc. and fix the faults, problems if any. • For roof, gutters etc, remove the leaves, branches of trees or other debris. Keep the lid always in

poison. • Before collecting rain water in the tank, allow the water from first 6-8 minutes rain to go waste to

ensure harvesting of the clean rain water only. If necessary, allow more time until clean water is observed in the waste water outlet.

• Prevent wastage of water through open taps and leakage. • Fill the tank to the brim with the last rains of the season. • During dry season, rain is few and far between .so must be taken that darts and pollutants from

roof, gutter, inlet point etc. are allowed to go to waste with first 10-15 minutes. • When the tank is fully empty and dry, paint or white wash the tank if necessary. • With the first rain of season fill the tank entirely with clean rain water only and for disinfecting

the tank pour a solution of bleaching powder (200 grams of bleaching powder Ca(Ocl)Ca dissolved in one bucket of water) in the tank stir vigorously with a clean stick. This water is stand for 24-hour in the tank and pass out this water as waste water.

B. Water quality Monitoring: Physical, chemical and bacteriological qualities of rainwater are usually good, if collected hygienically. As full proof hygienic collection and storage is not possible, there are chances of pollution particularly during collection in view of this a minimum water quality monitoring programmed must be implemented. By Daily monitoring we can Turbidity, Color. Clean rainwater must be free from odor and taste. Once every week


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well carry out test on this parameter. At the rain water harvesting unit site odor and taste can be tested by smelling by nose and test by testing of tongue. C. Insect vector Monitoring: Most mosquitoes remain close to the lake, pond or clogged gutter. Rainy season provides plenty of breeding places for them. Mosquitoes are good vector of many serious diseases and it is the only vector of some diseases such as- Malaria, Heart worm, Yellow fever, Dengue, fever, Encephalitis.

• Avoid all the factors which result in attracting mosquitoes. • Tightly closed lids may be provided to the water storage system, so that there are no openings for

the entry of mosquitoes. • Filter should be disinfected (e.g. with household bleach). • No stagnating water should be allowed around the rain water harvesting site. • Gutter leading to the storage should have a free flow of water.

Cost Consideration: It is preferable to construct the tank using brick and RCC. The will be in between 10,000-12,000/= taka. Although its initial cost is high then other RWHS but the cost of water we can collect is low then others. All the filter media and chemical are using here is low cost and available. RWHS for cities-A new hope: Although RWHS is mostly practiced in coastal areas and areas with arsenic contaminated ground water in the context of Bangladesh, it may be a new hope for the cities where the authority is failing to supply water as demanded. In Bangladesh there is a deficit of supply of water by WASA in almost all cities, specifically in Dhaka. This deficit may be recovered by the application of RWHS. Here the roles of Architects are mostly superior because they are the designer of building look. As we all know catchments area is one of the most important component of RWHS, this catchments area need to be suited for a buildings view. If architects of Bangladesh now starts there new mission of building design with the idea of RWHS it is sure that RWHS will become a common practice for most cities of Bangladesh with the new hope to face the water scarcity. Conclusions and Recommendation Arsenic contamination in ground water in Bangladesh is so acute that it demands an immediate solution. In order to address the arsenic problem, different government and non-government organizations are coming up with a number of solutions. But no sustainable, acceptable and affordable solution has yet been adopted. This Rain Water Harvesting System has been providing the opportunity to develop appropriate and usable rainwater harvesting as a sustainable solution to address the arsenic problem. It is quite optimistic to yield highly productive outcomes from this action research project, which would establish the fact that the RWHS does indeed possess much potentiality of becoming a suitable, sustainable, affordable, socially acceptable and viable alternative source for safe drinking water, which can be widely promoted throughout different geo-hydrological areas of Bangladesh. References 1.Texas Water Development Board 1997 Texas Guide to Rainwater Harvesting, Austin Texas 2.Lanka rainwater harvesting forum 2000, Current rural water security practices with DRWH, SRI LANKA 3. http://www.eng.warwick.ac.uk/DTU/rainwaterharvesting/index.html Report A1 - Current Technology for Storing Domestic Rainwater (Part 1) 4. NGO Forum for Drinking water Supply and Sanitation Rainwater Harvesting System- an action research project

Rain Water Harvesting Comparison Between Existing Techniques and Its Modification_Mohammad Ali

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