Rain Water Harvesting for the Individual Houses

Roof top rain water can be diverted to the existing open / bore well. Along with this, rain water available in the open spaces around the building may be recharged into the ground through the following simple effective methods.

Percolation pits (Small houses)
Recharge Trench (Big houses / Apartments)
Recharge wells (Large buildings / industries)

Based on the size /area of the building and the underlying lithological nature of the formation the said methods may be used either individually or in combinations.

To enhance nature recharge of rain water avoid pavements since unpaved surfaces have more percolation rate.

Various Methods of Recharging In Individual Houses

Percolation Pit Method

Bore Well with Settlement Tank

Open Well Method with filter bed Sump

Percolation Pit with Bore Method Click for more Information :)

Components of Rooftop Rainwater Harvesting System

In domestic Rooftop Rainwater Harvesting Systems rainwater from the house roof is collected in a storage vessel or tank for use during the periods of scarcity. Usually these systems are designed to support the drinking and cooking needs of the family at the doorstep. Such a system usually comprises a roof, a storage tank and guttering to transport the water from the roof to the storage tank. In addition, a first flush system to divert the dirty water which contains roof debris collected on the roof during non-rainy periods and a filter unit to remove debris and contaminants before water enters the storage tank are also provided. Therefore, a typical rooftop Rainwater Harvesting System comprise of following components:

· Roof catchment
· Gutters
· Down pipe and first flush pipe
· Filter unit
· Storage tank
· Collection pit

Among the above components, storage tank is the most expensive and critical component. The capacity of the storage tank determines the cost of the system and reliability of the system for assured water supply. Following is the brief description of each component with a study of different materials used for each component.

Roof Catchment:
The roof of the house is used as the catchment for collecting the rainwater. The style, construction and material of the roof affect its suitability as a catchment. Roofs made of corrugated iron sheet, asbestos sheet, tiles or concrete can be utilized as such for harvesting the rainwater. But thatched roofs are not suitable as it gives some colour to water and also the water carries pieces of roof material (such as palm leaves).

Gutters:
Gutters are channels fixed to the edges of roof all around to collect and transport the rainwater from the roof to the storage tank. Gutters can be prepared in semi-circular and rectangular shapes as shown in figures. Locally available material such as plain galvanized iron sheet can be easily folded to required shapes to prepare semi-circular and rectangular gutters. Semi-circular gutters of PVC material can be readily prepared by cutting the PVC pipes into two equal semi-circular channels. Bamboo poles can also be used for making gutters if they are locally available in sufficient quantity. Use of such locally available materials reduces the overall cost of the system.

Downpipe and First Flush Pipe:
Downpipe:
Down pipe is the pipe, which carries the rainwater from the gutters to the storage tank. Down pipe is joined with the gutters at one end, and the other end is connected to the filter unit of the storage tank as shown in figure below. PVC or GI pipes of diameter 50 mm to 75 mm (2 inch to 3 inch) are commonly used for down-pipe. Bamboo can also be used wherever available in suitable size.

First Flush Pipe:
Debris, dirt and dust collect on the roofs during non-rainy periods. When the first rains arrive, this unwanted material will be washed into the storage tank. This caused contamination of water collected in the storage tank thereby rendering it unfit for drinking and cooking purposes.
Therefore, a first flush system is incorporated in the Rooftop Rainwater Harvesting Systems to dispose off the 'first flush' water so that it does not enter the tank. There are two such simple systems. One is based on a simple manually operated arrangement, whereby, the down pipe is moved away from the tank inlet and replaced again once the first flush water has been disposed.
In another simple and semi-automatic system, a separate vertical pipe is fixed to the down pipe with a valve provided below the "T" junction as shown in figure.
After the first rain is washed out through first flush pipe, the valve is closed to allow the water to enter the down pipe and reach the storage tank.

Filter Unit:
The filter unit is a container or chamber filled with filter media such as coarse sand, charcoal, coconut fibre, pebbles and gravels to remove the debris and dirt from water that enters the tank. The container is provided with a perforated bottom to allow the passage of water. The filter unit is placed over the storage tank. Commonly used filters are of two types. One is a ferrocement filter unit, which is comparatively heavy and the other is made of either aluminium or plastic bucket. The latter is readily available in market and has the advantage of ease in removing, cleaning and replacing.
Another simple way of filtering the debris and dust particles that came from the roof along with rainwater is to use a fine cloth as filter media. The cloth, in 2 or 3 layers, can be tied to the top of a bucket or vessel with perforations at the bottom.

Storage Tank:
Storage tank is used to store the water that is collected from the Rooftops. Common vessels used for small scale water storage are plastic bowls, buckets, jerry cans, clay or ceramic jars, cement jars, old oil drums etc. For storing larger quantities of water the system will usually require a bigger tank with sufficient strength and durability.

There are unlimited number of options for the construction of these tanks with respect to the shape (cylindrical, rectangular and square), the size (Capacity from 1,000 lt. to 15,000 lt. or even higher) and the material of construction (brickwork, stonework, cement bricks, ferrocement, plain cement concrete and reinforced cement concrete). For domestic water needs, taking the economy and durability of tanks into consideration, ferrocement tanks of cylindrical shape in capacities ranging between 4,000 lt. and 15,000 lt. are most suitable. Plain cement concrete and reinforced cement concrete are used for tank capacities usually more than 50,000 lt. Brick, stone, cement brick may be used for capacities ranging between 15,000 lt. to 50,000 lt.
The ferrocement tanks are usually constructed above ground level because of the advantages, such as, a) ease in finding structural problems/leaks, b) easy to maintain and clean and c) easy to draw water. It is difficult to detect the leaks and take corrective measures in case of underground tanks. Water from underground tanks cannot be drawn by gravity. Some kind of manual or power lifting devices need to be used for drawing the water. Further, in coastal areas, underground tanks are prone to water contamination due to fluctuation in groundwater table and leakage of stored water.

The storage tank is provided with a cover on the top to avoid the contamination of water from external sources. The cover will be in dome shape having a raise of about 20-30 cm. in the middle. The dome is provided with two circular openings, one for manhole and another for accommodating the filter. A lid covers the manhole avoiding exposure of stored water to the outside environment. The storage tank is provided with pipe fixtures at appropriate places to draw the water, to clean the tank and to dispose of the excess water. They are named tap or outlet, drainpipe and over flow pipe respectively. PVC or GI pipes of diameter 20 mm to 25 mm (¾ inch to 1 inch) are generally used for this purpose.

Collection Pit:
A small pit is dug in the ground, beneath the tap of the storage tank and constructed in brick masonry to make a chamber, so that a vessel could be conveniently placed beneath the tap for collecting water from the storage tank. A small hole is left at the bottom of the chamber, to allow the excess water to drain-out without stagnation. Size of collection pit shall be 60 cm x 60 cm x 60 cm.

COMPONENTS OF A RAINWATER HARVESTING SYSTEM

 Continued... 

8. Recharge structures

Rainwater may be charged into the groundwater aquifers through any suitable structures like dugwells, borewells, recharge trenches and recharge pits.

Various recharge structures are possible - some which promote the percolation of water through soil strata at shallower depth (e.g., recharge trenches, permeable pavements) whereas others conduct water to greater depths from where it joins the groundwater (e.g. recharge wells). At many locations, existing structures like wells, pits and tanks can be modified as recharge structures, eliminating the need to construct any structures afresh. Here are a few commonly used recharging methods:

1. Recharging of dugwells and abandoned tubewells.
In alluvial and hard rock areas, there are thousands of wells which have either gone dry or whose water levels have declined considerably. These can be recharged directly with rooftop run-off. Rainwater that is collected on the rooftop of the building is diverted by drainpipes to a settlement or filtration tank, from which it flows into the recharge well (borewell or dugwell).

If a tubewell is used for recharging, then the casing (outer pipe) should preferably be a slotted or perforated pipe so that more surface area is available for the water to percolate. Developing a borewell would increase its recharging capacity (developing is the process where water or air is forced into the well under pressure to loosen the soil strata surrounding the bore to make it more permeable).

If a dugwell is used for recharge, the well lining should have openings (weep-holes) at regular intervals to allow seepage of water through the sides. Dugwells should be covered to prevent mosquito breeding and entry of leaves and debris. The bottom of recharge wells should be desilted annually to maintain the intake capacity.

Providing the following elements in the system can ensure the quality of water entering the recharge wells:
1. Filter mesh at entrance point of rooftop drains
2. Settlement chamber
3. Filter bed

A settlement chamber

2. Settlement tank
Settlement tanks are used to remove silt and other floating impurities from rainwater. A settlement tank is like an ordinary storage container having provisions for inflow (bringing water from the catchment), outflow (carrying water to the recharge well) and overflow. A settlement tank can have an unpaved bottom surface to allow standing water to percolate into the soil.

In case of excess rainfall, the rate of recharge, especially of borewells, may not match the rate of rainfall. In such situations, the desilting chamber holds the excess amount of water till it is soaked up by the recharge structure. Thus, the settlement chamber acts like a buffer in the system.

Any container, (masonry or concrete underground tanks, old unused tanks, pre-fabricated PVC or ferrocement tanks) with adequate capacity of storage can be used as a settlement tank.

3. Recharging of service tubewells.
In this case the rooftop runoff is not directly led into the service tubewells, to avoid chances of contamination of groundwater. Instead rainwater is collected in a recharge well, which is a temporary storage tank (located near the service tubewell), with a borehole, which is shallower than the water table. This borehole has to be provided with a casing pipe to prevent the caving in of soil, if the strata are loose. A filter chamber comprising of sand, gravel and boulders is provided to arrest the impurities.

4. Recharge pits
A recharge pit is 1.5m to 3m wide and 2m to 3m deep. The excavated pit is lined with a brick/stone wall with openings (weep-holes) at regular intervals. The top area of the pit can be covered with a perforated cover. Design procedure is the same as that of a settlement tank.

5. Soakaways / Percolation pit

Filter materials in a soakaway

Percolation pits, one of the easiest and most effective means of harvesting rainwater, are generally not more than 60 x 60 x 60 cm pits, (designed on the basis of expected runoff as described for settlement tanks), filled with pebbles or brick jelly and river sand, covered with perforated concrete slabs.

6. Recharge trenches
A recharge trench is a continuous trench excavated in the ground and refilled with porous media like pebbles, boulders or broken bricks. A recharge trench can be 0.5 m to 1 m wide and 1 m to 1.5 m deep. The length of the recharge trench is decided as per the amount of runoff expected. The recharge trench should be periodically cleaned of accumulated debris to maintain the intake capacity. In terms of recharge rates, recharge trenches are relatively less effective since the soil strata at depth of about 1.5 metres is generally less permeable. For recharging through recharge trenches, fewer precautions have to be taken to maintain the quality of the rainfall runoff. Runoff from both paved and unpaved catchments can be tapped.

7. Recharge troughs

Source: A water harvesting manual for urban areas

To collect the runoff from paved or unpaved areas draining out of a compound, recharge troughs are commonly placed at the entrance of a residential/institutional complex.These structures are similar to recharge trenches except for the fact that the excavated portion is not filled with filter materials. In order to facilitate speedy recharge, boreholes are drilled at regular intervals in this trench. In design part, there is no need of incorporating the influence of filter materials.
This structure is capable of harvesting only a limited amount of runoff because of the limitation with regard to size.

8. Modified injection well
In this method water is not pumped into the aquifer but allowed to percolate through a filter bed, which comprises sand and gravel. A modified injection well is generally a borehole, 500 mm diameter, which is drilled to the desired depth depending upon the geological conditions, preferably 2 to 3 m below the water table in the area. Inside this hole a slotted casing pipe of 200 mm diameter is inserted. The annular space between the borehole and the pipe is filled with gravel and developed with a compressor till it gives clear water. To stop the suspended solids from entering the recharge tubewell, a filter mechanism is provided at the top.

COMPONENTS OF A RAINWATER HARVESTING SYSTEM

CONTINUED...

Filter for large rooftops
When rainwater is harvested in a large rooftop area, the filtering system should accommodate the excess flow. A system is designed with three concentric circular chambers in which the outer chamber is filled with sand, the middle one with coarse aggregate and the inner-most layer with pebbles.This way the area of filtration is increased for sand, in relation to coarse aggregate and pebbles. Rainwater reaches the centre core and is collected in the sump where it is treated with few tablets of chlorine and is made ready for consumption. This system was designed by R Jeyakumar

Varun:
S Vishwanath, a Bangalore water harvesting expert, has developed a rainwater filter "VARUN". According to him, from a decently clean roof 'VARUN' can handle a 50 mm per hour intensity rainfall from a 50 square metre roof area. This means the product is relatively standardised. For new house builders we therefore can recommend the number of downpipes they have to optimise on and the number of filters they will need.

'VARUN' is made from a 90 litre High Density Poly Ethylene (HDPE) drum. The lid is turned over and holes are punched in it. This is the first sieve which keeps out large leaves, twigs etc. Rainwater coming out of the lid sieve then passes through three layers of sponge and a 150 mm thick layer of coarse sand. Presence of sponge makes the cleaning process very easy. Remove the first layer of sponge and soak /clean it in a bucket of water (which you then don't waste but use it for plants). The sand needs no cleaning at all. The basic cost of the filter is about Rs 2250/-

Filters available in the German Market
According to Wessels (1994), concerns over the possible negative health effects of rainwater utilisation led to some opposition. The Federal Office of Health, for example, initially objected to its use for washing clothes, personal hygiene and even for toilet flushing, due to possible risks of infection and allergic reactions. Long-term investigations by the health offices in Hamburg and Bremen, however, have yielded positive results with respect to the use of water for washing purposes and have confirmed that rainwater sources do not present a health risk.

(i) Filters developed by WISY
Private companies such as WISY, based in Kefenrod in Germany, and are playing an important role in promoting rainwater use by developing pumps and filter devices to improve water quality. WISY has developed a simple filter system, which can be attached to a standard household downpipe. Under conditions in Germany (assuming a mean annual rainfall of 650mm/year), this can divert and filter 90 per cent of the runoff from a roof area of up to 200 square metre.

(a)

(fig a). A filter collector diverts 90 per cent of rainwater to a storage tank through a 0.17 mm stainless steel mesh filter.

(b)

(fig b). A larger vortex fine filter can cope with run-off from roof areas of up to 500 square metres.

(c)

(fig c). A floating fine suction filter for ensuring that the water pumped from the tank is extracted from the cleanest part of the tank and is free of particulates has also been developed.

For details contact:
WISY (Winkler system)
OT Hitzkirchen, Oberdorfstrasse 26,
D-63699, Kefendrod-Hitzkirchen
Germany; fax:+60-54-912129
Wisyag@t-online.de
(Source: John Gould and Erik Nissen-Petersen, 1999: Rainwater Catchment Systems for Domestic Supply - Design, Construction and Implementation, Intermediate Technology Group)

(ii) Filters developed by MALLBETON
Another company, MALLBETON, a manufacturer of concrete tanks and filters, based in Germany, are marketing a tank design which manages any overflows (Konig, 1998). This is done by constructing the top half of a sub-surface tank from a porous concrete ring, which allows water to gradually seep into the ground. While this reduces the volume of water available, it does make householders eligible for waivers on their rainwater drainage fees. These fees are already applied to householders and businesses in about 25 per cent of Germany. The charges that are levied on each square metre of roof area and sealed surroundings can be substantial, such as in Bonn, so waivers often provide significant savings.
(Source: John Gould and Erik Nissen-Petersen, 1999: Rainwater Catchment Systems for Domestic Supply - Design, Construction and Implementation, Intermediate Technology Group)

 THAT IS ALL ON FILTERS...

COMPONENTS OF A RAINWATER HARVESTING SYSTEM

Continued....

6. Filter
The filter is used to remove suspended pollutants from rainwater collected over roof. A filter unit is a chamber filled with filtering media such as fibre, coarse sand and gravel layers to remove debris and dirt from water before it enters the storage tank or recharges structure. Charcoal can be added for additional filtration.

Source: A water harvesting manual for urban areas

(i) Charcoal water filter
A simple charcoal filter can be made in a drum or an earthen pot. The filter is made of gravel, sand and charcoal, all of which are easily available.
(ii) Sand filters
Sand filters have commonly available sand as filter media. Sand filters are easy and inexpensive to construct. These filters can be employed for treatment of water to effectively remove turbidity (suspended particles like silt and clay), colour and microorganisms.

Source: A water harvesting manual for urban areas

In a simple sand filter that can be constructed domestically, the top layer comprises coarse sand followed by a 5-10 mm layer of gravel followed by another 5-25 cm layer of gravel and boulders.

(ii. a) Dewas filters
Most residents in Dewas, Madhya Pradesh, have wells in their houses. Formerly, all that those wells would do was extract groundwater. But then, the district administration of Dewas initiated a groundwater recharge scheme. The rooftop water was collected and allowed to pass through a filter system called the Dewas filter, designed by Mohan Rao, district collector of Dewas, and engineers of the rural engineering services. The water thus filtered is put into the service tube well.

         The filter consists of a polyvinyl chloride (PVC) pipe 140 mm in diameter and 1.2m long. There are three chambers. The first purification chamber has pebbles varying between 2-6 mm, the second chamber has slightly larger pebbles, between 6 and 12 mm and the third chamber has the largest - 12-20 mm pebbles. There is a mesh at the outflow side through which clean water flows out after passing through the three chambers. The cost of this filter unit is Rs 600.

ii. b. Horizontal roughing filter and slow sand filter
The introduction of horizontal roughing filter and slow sand filter (HRF/SSF) to treat surface water has made safe drinking water available in coastal pockets of Orissa. The major components of this filter are described below.1) Filter channel : One square metre in cross-section and eight m in length, laid across the tank embankment, the filter channel consists of three uniform compartments, the first packed with broken bricks, the second with coarse sand, followed by fine sand in the third compartment. The HRF usually consists of filter material like gravel and coarse sand that successively decreases in size from 25 mm to 4 mm. The bulk of solids in the incoming water are separated by this coarse filter media or HRF. At every outlet and inlet point of the channel, fine graded mesh is implanted to prevent entry of finer materials into the sump. The length of a channel varies according to the nature of the site selected for the sump.2) Sump: A storage provision to collect filtered water from the tank through the filter channel for storage and collection.

While HRF acts as a physical filter and is applied to retain solid matter, SSF is primarily a biological filter, used to kill microbes in the water. Both filter types are generally stable, making full use of the natural purification process of harvested surface water and do not require any chemicals.

For more details:
Making Water Everybody's Business

iii. Rain PC
AcquaSure, a consortium of three specialist Netherlands-based companies, has developed a system for the conversion of rainwater to drinking water in the form of a Rainwater Purification Centre (RainPC).

RainPC is developed by scaling down the multi-staged water treatment method (MST), which involves screening, flocculation sedimentation and filtration and incorporating existing technologies like upward flow fine filtration, absorption and ion exchange. Coming in a small compact 26 kg unit, the RainPC offers an affordable solution by converting rainwater into drinking water.

RainPC is made of ultra violet resistant poly-ethylene housing and cover, stainless steel rods and bolts, a nickel-brass valve and an adapter for maintaining constant volume. Xenotex-A and activated carbon catridges along with ultra membrane filtration or micro-membrane filtration modules incorporated in the RainPC has the capacity to deal with E-coli and the potential of meeting the Dutch as well as World Health Organisations (WHO) water regulation standards. The components can also be transported individually to be assembled at the site. Three product types are available based on their microbial contaminant removal capacity. This technology is ideally suited for virtually any situation and is a blessing particularly for those who have little or no access to regular safe drinking water.

iv. Rainwater harvester
EA Water Pvt Ltd has launched a unique Rainwater Harvester, which filters runoff water from roads, which generally contains oil and grease. This system has been installed in the Gymkhana club, Sector-15, Faridabad, Haryana. Rajit Malohtra, project in charge, of this company explained that the water harvesting system installed at the club has a sand filter, which filters silt from runoff harvested from roof, lawns and parking area. The cost of the filter is around Rs 60,000.

TO BE CONTINUED... J

Source: A water harvesting manual for urban areas

COMPONENTS OF A RAINWATER HARVESTING SYSTEM

A rainwater harvesting system comprises components of various stages - transporting rainwater through pipes or drains, filtration, and storage in tanks for reuse or recharge. The common components of a rainwater harvesting system involved in these stages are illustrated here. 1. Catchments: The catchment of a water harvesting system is the surface which directly receives the rainfall and provides water to the system. It can be a paved area like a terrace or courtyard of a building, or an unpaved area like a lawn or open ground. A roof made of reinforced cement concrete (RCC), galvanised iron or corrugated sheets can also be used for water harvesting.

2. Coarse mesh at the roof to prevent the passage of debris
3. Gutters:
Channels all around the edge of a sloping roof to collect and transport rainwater to the storage tank. Gutters can be semi-circular or rectangular and could be made using:

• Locally available material such as plain galvanised iron sheet (20 to 22 gauge), folded to required shapes.
                                                                                                                                                                                                                                 Source: A water harvesting manual for urban areas
• Semi-circular gutters of PVC material can be readily prepared by cutting those pipes into two equal semi-circular channels.
• Bamboo or betel trunks cut vertically in half.

The size of the gutter should be according to the flow during the highest intensity rain. It is advisable to make them 10 to 15 per cent oversize.

Gutters need to be supported so they do not sag or fall off when loaded with water. The way in which gutters are fixed depends on the construction of the house; it is possible to fix iron or timber brackets into the walls, but for houses having wider eaves, some method of attachment to the rafters is necessary.

4. Conduits
Conduits are pipelines or drains that carry rainwater from the catchment or rooftop area to the harvesting system. Conduits can be of any material like polyvinyl chloride (PVC) or galvanized iron (GI), materials that are commonly available.

The following table gives an idea about the diameter of pipe required for draining out rainwater based on rainfall intensity and roof area:

Diameter Of pipe (mm)	Average rate of rainfall in mm/h
	50	75	100	125	150	200
50	13.4	8.9	6.6	5.3	4.4	3.3
65	24.1	16.0	12.0	9.6	8.0	6.0
75	40.8	27.0	20.4	16.3	13.6	10.2
100	85.4	57.0	42.7	34.2	28.5	21.3
125	-	-	80.5	64.3	53.5	40.0
150	-	-	-	-	83.6	62.7

Source: National Building Code

5. First-flushing
A first flush device is a valve that ensures that runoff from the first spell of rain is flushed out and does not enter the system. This needs to be done since the first spell of rain carries a relatively larger amount of pollutants from the air and catchment surface.

Source: A water harvesting manual for urban areas

TO BE CONTINUED.... :)