Necessity Of Rain Water Harvesting :-

                         Shortage of potable water supply in urban areas is one of the main problems which is being faced by all countries including developed countries of the world. Human beings can not survive without water even for a day. The underground water is depleting day by day everywhere, whereas population of urban areas is increasing at alarming rate, mainly, due to migration of population from rural areas to urban areas and hence increasing the demand of water. In urban areas, the charging of  underground water in natural way like rural areas is not taking place due to large sprawl of urban settlements. Moreover, due to non charging of rain water during rainy season, the urban areas are causing heavy floods. These floods destroy urban infrastructure and crops of suburban areas every year during rainy season. Hence, there is a necessity to propagate   harvesting of  rain water in urban areas. 

                        The water which reaches to us through rain is absolutely free of cost,  sweet,  pure and is full of minerals. The method through which rain water is saved to recharge underground aquifers and stored for use later on, is known as rain water harvesting.  Rain Water Harvesting is a way to capture the rain water when it rains and store that water above ground or charge the underground for its later on use. The rainwater harvesting happens naturally in open rural areas, but in constructed, metalled and  over-paved urban areas / metropolitan cities, there is a need to harvest rain water through modern technique. The decision for storing and recharging water depends on the rainfall pattern of a particular region. The formation of under ground strata and geology of the area also play  an important role for charging rain water.  At places, where sub-strata is impermeable, recharging is not a feasible idea.

                        The stored water, collected from the road, is enough for watering the plants in lawns of Schools, Colleges, Hospitals and Institutional Areas where more than 70 % area is kept in the form of open spaces.  Rainwater is good for plants because it is free of salts and other minerals that harm root growth .As rainwater percolates into the soil, it forces salts down and way from root zones, allowing roots to grow better and making plants more drought tolerant.

Rain Water Harvesting Techniques:-

In Urban areas rain water harvesting can be divided into two categories as described below.

 ( A ) Rooftop Rainwater Harvesting :-

The rooftop rain water harvesting system requires four elements i.e. a catch-ment area, (ii) conduits, (iii) settlement tank and (iv) recharge or storage facility. For rain water harvesting system, a dried  bore well, an underground tank or soak pit are required  along with conduits or the pipes carrying rain water from the catchment or roof tops to harvesting/storage system.  

( 1 ) Roof Catchment:
The roof of the house is used as the catchment for collecting the rainwater. The style, construction and material of the roof effect 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).

(2) 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. 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 reduce the over all cost of the system.

(3) Down pipe:
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.

(4) 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, where by, 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. 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.

(5) Filter Unit:
The filter unit is a container or chamber filled with filter media such as coarse sand, charcoal, coconut fiber, pebbles and gravels to remove the debris and dust 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 fibrocement filter unit, which is comparatively heavy and the other is made of either aluminum 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.

(6) Storage Tank:
Storage tank is used to store the water that is collected form 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.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.

(7) 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 water.

(B) Storm  Water Recharging Through Open Drains ;

In urban areas natural way rain water harvesting occurs only in areas left out for open spaces and parks.  In the new areas which are being developed by the Urban Development Authorities / Civic bodies, the storm water is disposed off through underground channels of sewer lines, thus leaving no scope for recharging of this rain water into the earth.  The old technique of disposal of storm water through open drains is considered more environment friendly as through these open drains storm water charging take place in natural way.

Rooftop Rainwater Harvesting Should Be Made Compulsory Through Enforcement Of Building Bye Laws :

Adoption of roof top harvesting system is not a traditional culture of people living in urban areas. The problem of water scarcity and urban flooding can not be solved without the adoption of roof top rain water harvesting system. For the promotion of this system, all Governments and Civic Bodies should make necessary provisions in the Building Bye Laws and should enforce the said Building Bye Laws rigorously.

The Haryana Government has made a step forward in this direction by making necessary provisions in the Building Bye Laws enacted under the Punjab Scheduled Roads and Controlled Areas Restrictions of Unregulated Development  Rules  1963. Under the said Rules, the harvesting of rain water has become a liability for all prioprioters having property of covered area more than 100 square meters. The said Rules are described as below.  

(1)       Arrangement of roof top rain water harvesting will have to be made by the plot-owners on the plots in the buildings constructed in the colonies for which licence has been granted under Act No. 8 of 1975, or where permission for change of land use has been permitted and where the area of the roof is 100 square meters or more.

(2)       The system of collection, conveyance and dispersion of rain water for harvesting shall be made in such a manner that only clear water is able to enter.  No contaminated / waste water from the building or surrounding areas should find its way into the system.

(3)       The entry points of the rain water for harvesting shall be designed in such a manner that in normal days these remain covered.  Arrangement of segregation of the rain water from the first shower (containing the wash water) should also be provided.

(4)       The arrangement for quick filtration of rain water shall also be made in the rain water harvesting well/tube-well, so that the rain water does not pollute or choke the strata.

(5)       The complete system of rain water harvesting will be constructed within the area of the plot, defined in the zoning plan for the plot.

(6)       The recharge well shall be located at a distance of not less than ten meters away from any structure handling sewage or industrial waste water (such as septic tank or effluent treatment plant).  This minimum distance of ten meters will not be applicable to manholes or sewer lines although it will be ensured that they are leak proof.

(7)       The detail proposal of the system comprising of collection, conveyance and dispersion of rain water from the roof top to rain water harvesting well/tube-well will have to be shown on the building plan submitted for approval.

(8)       Any engineer not below the rank of an Executive Engineer so authorized by the Director, Town and Country Planning  will have the powers to inspect the system whenever considered necessary and direct the owner of the building to affect any changes/improvement as deemed necessary and the owner of the building shall ensure compliance.

 (9)       Depending upon the underground water strata, the Government may notify certain areas where provision of such rain water harvesting system may not be required.  Broad guidelines about the approximate depth of the recharge well and the sample strata chart will also be made available.