When people are striving for drinking water and ground water table is going lower and lower every year, we have to seriously think about Rainwater Harvesting, especially in the urban areas. In our earlier article Rainwater Harvesting, we discussed about it and its advantages. Now we will discuss here the methods of rainwater harvesting, which can be installed at our home.
There are three methods of harvesting rainwater as given below:
1) Storing rainwater for direct use
2) Recharging ground water table
1) Storing rain water for direct use
If the ground strata is impermeable or the ground water is saline/unfit for human consumption or ground water table is very deep, this method of rainwater harvesting is preferred. In this method, the rainwater collected from roof top is filtered and then stored in storage tanks for direct use.
2) Recharging ground water table
This method of rainwater harvesting is adopted in the areas where the rainfall occurs only for a short period say for 2-3 months in a year and water table is at a shallow depth. In this method rain water that is collected from the roof top of the building and diverted by drain pipes to a filtration tank from which it flows into the recharge well. The recharge well should preferably be shallower than the water table.
a) Through recharge pit
It is adopted for buildings having roof area up to 100 sqm. Recharge pit of any shape is constructed generally 1-2 m wide and 2-3 m deep. The pit is filled with boulders, gravel and sand for filtration of rain water. Top layer of sand of filter should be cleaned periodically for better ingression of rain water in to the sub soil. It should be ensured that water entering into the recharge pit is silt free.
b) Recharge through abandoned dug well / open well
It is suitable for buildings having a roof top area more than 100 sqm . In this method, a dry / unused dug well can be used as a recharge structure. After filtration, the water is guided through a pipe of 100 mm to the bottom of the well. Well cleaning and de-silting is very important before using it. Well should be cleaned periodically and chlorinated to control bacteriological contamination.