Water scarcity is serious problem throughout the world for both urban and rural community. Rainwater harvesting is defined as process of augmenting the natural infiltration of rainwater or surface water into the ground by some artificial methods. In rooftop harvesting, the roof becomes the catchments and the rainwater is collected from the roof of the house/building it can either be stored in a tank or diverted to recharge pit etc. This method is less expensive and very effective and if implemented properly helps in augmenting the ground water level of the area. The methods of rooftop rainwater harvesting are recharge pit, recharge trenches, storage tanks, abandoned dug wells, bore well. The main source of water is rain and if this rain water is agglomerated and harvested, the scarcity of water in water scarce region can be minimized even to the extent of elimination. One of the major panaceas in water scarce area where there is inadequate groundwater supply in terms of quantity and quality can be resolve by the technique of rain water harvesting. In urban areas, rain water available from rooftop of buildings and paved road during monsoon goes as a waste. This water can be stored in tank and can be used directly or indirectly by diverting to treatment plant through various ground water tapping arrangements and catchments which in turn can be utilized at the time of need.
Rainwater harvesting (RWH) is the collection and storage of rain, rather than allowing it to run off. Rainwater is collected from a roof-like surface and redirected to a tank, cistern, deep pit (well, shaft, or borehole), aquifer or a reservoir with percolation, so that it seeps down and restores the ground water. Dew and fog can also be collected with nets or other tools. Rainwater harvesting differs from storm water harvesting as the runoff is typically collected from roofs and other surfaces for storage and subsequent reuse. Its uses include watering gardens, livestock irrigation domestic use with proper treatment, and domestic heating. The harvested water can also be committed to longer-term storage or groundwater recharge Rainwater harvesting is one of the simplest and oldest methods of self-supply of water for households having been used in South Asia and other countries for many thousands of years.
A. Methods of Rainwater Harvesting
Broadly there are two types of RWH
Surface run off harvesting
Roof top rain water harvesting
B. Rooftop Rain Water Harvesting
The rain water which is flowing off from rooftops of residential, institutional, industrial and various other buildings is collected and stored for further use is termed as rooftop rain water harvesting. Rooftop Rain Water Harvesting is the technique through which rain water is captured from the roof catchments and stored in reservoirs. Harvested rain water can be stored in sub-surface ground water reservoir by adopting artificial recharge techniques to meet the household needs through storage in tanks. The Main Objective of rooftop rain water harvesting is to make water available for future use. The use may be temporary, seasonal or permanent except in years of exceptionally low rainfall. The rain water from the roof may also be used for recharging the ground water through nearby water sources such as open dug wells or bore wells. In terms of economic and human welfare it has a crucial role to play. Rainwater in many cases is most reliable, easiest to access, and least polluted source. It can be collected and controlled by the individual household or community as it is not open to abuse by other users.
Some of the following advantages are
Provides self-sufficiency to your water supply.
Cost investment for pumping of ground water is reduced.
Supply better and safer quality of water.
Improves the quality of ground water through dilution when recharged to groundwater.
Soil erosion can be eliminated and flooding in low lying area is avoided.
Comparatively less expensive.
This method is simple to adopt for all individuals.
It is easy to construct, operate and maintain.
C. Components of Rainwater Harvesting
Catchment: The surface that receives rainfall directly is the catchment of rainwater harvesting system. It may be a terrace, courtyard, or paved or unpaved open ground. The terrace may be a flat RCC/stone roof or sloping roof. Therefore the catchment is the area, which actually contributes rainwater to the harvesting system.
Transportation: Rainwater from the rooftop should be carried through down to take water pipes or drains to the storage/harvesting system. Water pipes should be UV resistant (ISI HDPE/PVC pipes) of the required capacity. Water from sloping roofs could be caught through gutters and down take the pipe. At terraces, the mouth of each drain should have wire mesh to restrict floating material.
First Flush: The first flush is a device used to flush off the water received in the first shower. The first shower of rains needs to be flushed-off to avoid contaminating storable/rechargeable water by the probable contaminants of the atmosphere and the catchment roof. It will also help in cleaning of silt and other material deposited on the roof during dry seasons. Provisions of first rain separators should be made at the outlet of each drain pipe.
Filter: There is always some skepticism regarding Roof Top Rainwater harvesting since doubts are raised that rainwater may contaminate groundwater. There is a remote possibility of this fear coming true if the proper filter mechanism is not adopted. Secondly, all care must be taken to see that underground sewer drains are not punctured, and no leakage is taking place in close vicinity. Filters are used for the treatment of water to effectively remove turbidity, color, and microorganisms. After the first flushing of rainfall, water should pass through filters. A gravel, sand, and ‘netlon’ mesh filter is designed and placed on top of the storage tank. This filter is very important in keeping the rainwater in the storage tank clean. It removes silt, dust, leaves, and other organic matter from entering the storage tank. The filter media should be cleaned daily after every rainfall event. Clogged filters prevent rainwater from easily entering the storage tank and the filter may overflow. The sand or gravel media should be taken out and washed before it is replaced in the filter.
Storage Structures: Storage structures are provided to store the filtered rain water for various activities. This stored rain water can also be used for recharging groundwater.
Design of Rainwater Harvesting System at MPCOE Campus
1) This project deals with all aspects of eradicating the water scarcity problem in MPCOE campus by implementing ancient old technique Rain Water Harvesting. The rain water collected from the roof is of sufficient quantity and thus, for this quantity the underground water tank capacity has been calculated for which the design can be made.
2) RCC tank is constructed underground in suitable area, so that the land about the above can be beneficial for other purposes. The tank of capacity 100000 litres is to be constructed in the campus.
3) Hence, it is finally concluded that adopting the Rain Water Harvesting in the campus of MPCOE will be the best approach towards harvesting rainwater and decrease the over dependence on the ground water.
 Review on Design of Rooftop Rainwater Harvesting in Nimgaon Village- A Case Study ofJunnar Tahsil Dr. P.D. Sabale, Prof. S.J.Yadawww.ijcrt.org
 Rain Water Harvesting Shaikh Ajim,KaduKrishna, Nedre Amolwww.irjet.net
 Rainwaterharvestingsystem1r.T.Londhe2S. S. Kadamwww.irjet.net
 Rain water harvesting – a case study in dr.AIT CAMPUS goutham HM1, hemanth kumarwww.irjet.net Water conservation: rain water harvesting project for college campus mr.S.S. Shinde1, prof P.A Hangarekarwww.irjet.net
 AMRUTAVARSHINI: A GUIDE FOR RAINWATER HARVESTING
 Rain water harvesting techniques to augment ground water, CENTRAL GROUND WATER BOARD
 Rainwater Harvesting Tool, SamSamWater Foundation
 Journal by J R Julius, Dr. R. Angeline on Rainwater Harvesting (RWH) - A review.
 RAIN WATER HARVESTING OF PIET CAMPUS – BY Bhupendersingh ofPIET and Sandeep Kumar of NIT Kurukshetr