In rural areas (village areas), most of the ground has open soil due to which rainwater can seep into the ground naturally to make up for the loss in groundwater due to excessive use. In urban areas (city areas), however, most of the ground is covered with buildings, concrete pavements and metalled roads due to which only very little rainwater seeps into the ground naturally.
Most of the rainwater which falls in cities flows into dirty water drains and goes away. So, rainwater harvesting is necessary in city areas. Rainwater harvesting by making more water percolate into the ground is usually done in those areas of a city where tube-wells for supplying water are located. This is to make sure that the tube-wells will never go dry.
The rainwater harvesting from open spaces around the buildings in a city is done by constructing percolation pits covered with concrete slabs having holes in them, and connected to a recharge well through a pipe. The recharge well is about 1 metre in diameter and 3 metres deep.
The rainwater falling in the open spaces around buildings goes into the percolation pit through the holes in its concrete slab cover. After filtration in percolation pit, rainwater enters the recharge well through the outlet pipe and gradually seeps into the soil. Please note that the purpose of recharge well is to collect the vast amount of water falling on the ground quickly when it rains and then make it seep into soil gradually. This groundwater can then be taken out through tube-wells as and when required. The advantage of rainwater harvesting is that it increases the availability of groundwater and helps in overcoming water shortage.