As the demand for water is actually more than the supply, there is an urgent need on our part to undertake rainwater harvesting on a serious note. In cities, more space is being utilized for construction of apartments to meet the housing needs of the ever-growing population. This has resulted in the exploitation of ground water source. A time has come where ground water is fast depleting and the government is unable to supply the required amount of water.
Rainwater harvesting is the system of collecting rainwater that flows on the surface, and utilizing the water for various purposes. Rainwater that falls on the terrace or roof is directed through a channel to a storage tank or a recharge pit in the ground. Rainwater harvesting is not a new concept. It has been practiced for many generations for irrigation and for feeding cattle and livestock.
It is important that the collected rainwater be kept clean and safe. The water from the first spell of rain should not be stored as it collects a large amount of dirt from the surface it flows on. For example, when rain water falls on the roof, the dirt and grime gets mixed with the water, which flows into the storage tank and contaminates the entire water. The same water when used is harmful. The first rain also carries pollutants from the air. It is advisable to install a first-flush diverter to divert water from the first spell of rain.
There are different ways of collecting rainwater. The most common method is using the down-pipe flap. This method lets the first flow of water through the down-pipe, while the water that flows later is let into the storage tank. A filter containing fiber, sand and gravel layers is installed to remove dirt and pollutants from the water that flows into the tank.
Rainwater harvesting is classified into roof catchment system and ground catchment system. Roof catchment system is common as it is easy to store rain water. Rain water that falls on the roof is collected in tanks or diverted to artificial recharge system using PVC pipes. Usually, rainwater collected from rooftops is not very dirty as compared to water collected from other surfaces. Ground water harvesting directs water from a prepared catchment area to another storage place. This system is generally used in areas where rainfall is less and where there are no other sources of water. This system is suitable for small communities rather than individual families.
Rainwater is also used for recharging ground water level. The rainwater collected is allowed be absorbed into the ground. This enables the ground water to recharge and keep the surrounding land moist and fertile.
Rainwater harvesting can be initiated in cities as it can be useful in many ways; provide water for the requirement of the city, increase soil moisture levels, improve ground water level, etc. The water collected through rainwater harvesting can be used for bathing, washing laundry and watering the garden.