Falling rain can provide some of the cleanest naturally occurring water that is available anywhere. There is considerable scope to collect rainwater when it falls, before it evaporates or becomes contaminated. RWH is not only a useful technology but also a good choice where groundwater is too deep of inaccessible due to hard ground condition, or where it is too silty, acidic, contaminated with arsenic, fluoride or otherwise unpleasant or unfit to drink.
How to harvest rain water?
The system is very simple; water drains from the roof into a drainpipe, which feeds into a storage tank fitted with a tap. The water is then safely stored right next to the house ready for use whenever needed or recharge groundwater aquifers. RWH systems are comprised of six basic components:
1. Catchments area upon which the rain falls
2. Gutters transport from catchments surface to storage
3. Screening bucket that removes debris
4. First-flush device to ensure that the runoff from the first spell of rain does not enter the system
5. Cisterns or Storage Tanks
6. Delivery system for the treated rainwater, either by gravity or pump
How much water can be harvested?
The amount of rainfall that can be effectively harvested is called the water harvesting potential. 25.4 mm (1 inch) of rainfall precipitation on one square foot of catchments surface can be calculated as 2.36 liters of water. However, in practice, this volume can never be achieved since a portion of the rainwater evaporates from the roof surface and a portion may be lost to the drainage system, including the first flush.
Therefore, we can only collect about 80% of the rainfall.
Quality of harvested rainwater
Collected rainwater is free of pollutants. However, it might be contaminated with air pollutants and surface contamination such as silt, dust etc. Biological contamination may occur if the rainwater catchment area is not cleaned. Flushing off the first 10-15 minutes of rainfall can prevent these contaminations
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