Rain Water Harvesting is essentially the capture of rainwater where it falls. There are two main techniques of rainwater harvesting, namely:
- Storage for future use
- Recharge into the ground
Water can be collected either from rooftops or from the ground or a combination of both. Rainwater harvesting systems can vary widely in scope and complexity. It can be the simple collection of rainwater from the rooftop of a house for use in gardening, or collection from a large school campus for use in the toilets or recharge into the ground.
Figure 1.1: Storage of rainwater Figure 1.2: Storage and recharge
Benefits of rainwater harvesting
Rainwater harvesting has a number of benefits both at an individual level and at the city-wide level.
- It would bring down consumer utility (water supply) bills and this is of great value especially to institutions, which spend considerable sums on water.
- Rainwater recharged into the ground would have a positive impact on groundwater quality through dilution of fluorides, nitrates and salinity. It would also stop the decline in groundwater levels.
- In coastal areas, where there is excessive groundwater extraction, recharge of rainwater into the ground would prevent sea-water ingress into fresh water aquifers.
- Urban flooding can be controlled if the residents of a city harvest rainwater from their rooftops for future use or take steps to effectively recharge groundwater within their premises.
- Using harvested rainwater reduces water demand from the municipality, which in turn reduces energy consumption in the water distribution network.
You must know…..
Recharge or infiltration is process of surface water seeping into the ground (from surface water systems and rain). The rate of recharge depends on the geology of the place. The rate of recharge would be very low through relatively impermeable materials like clay and shale and faster through more porous sandy soils.
Figure 1.5: SalineWater Intrusion
When it rains, only a portion of the water seeps into the ground. Most of it flows downhill over the land surface and is termed as runoff. Runoff is what keeps rivers and lakes full of water. Rainwater that flows off rooftops is called rooftop runoff.
Source: Rainwater Harvesting - Trainers’ Manual published by Karnataka Urban Infrastructure Development and Finance Corporation.