Water is a scarce natural resource in most regions of India.  Many city water supply administrations are spending huge amounts on transporting water from faraway places to the households. A new report (September, 2007) by the Planning Commissions http://www.thehindubusinessline.com/2007/09/19/stories/2007091952411000.htm) drawn attention to alarming depletion of groundwater at some places in India. Not to add the ongoing droughts.  

Over the last decade, various government organizations encouraged rain water harvesting, and there has been some progress in this area. For example, in Hyderabad and Chennai, it is compulsory to include rain water harvesting structure in house plans for approval. Also, there have been some projects on the revival of lakes and temple tanks to replenish ground water.

However, I think, it is time for us to accelerate our progress in the rain water harvesting and have concrete plans for future water demands. Most of the current rainwater harvesting programs concentrate on recharging ground water. I think there is enormous scope for harvesting roof water in underground tanks, and then use this water for residential applications AFTER PURIFICATION.

In my earlier studies on roof water harvesting possibilities of Center for Water Resources building (in Anna University campus, Chennai), it’s been noted that, if roof water is harvested (underground storage tank is available) it would supply sufficient water for domestic use to at least two more similar buildings.

Collecting roof water seems to be a simple process, no huge costs involved, however, purifying and pressuring for supply involves reasonable costs. Good amount of information and designs are available online (google it!) for roof water.  However, much information is not available on the quality of this harvested water and how to purify this water.

Water samples need to be collected from harvested water before domestic applications and need to be tested for physical, chemical and biological impurities. Table 1, presents The Bureau of Indian Standards (BIS 10500-1991) for drinking water in India.

Generally, the treatment process would include, but not limited to, screening, settling, filtering and disinfecting. The screening stage filters debris and large particles, the settling process then further cleans the rainwater by allowing the tiny particles that got through the screening process to settle at the bottom of the rainwater tank. Filtering is then supposed to remove sediment and contaminants and trap other smaller particles. The final process of disinfecting the rainwater can be done using chlorine, ozone or even ultraviolet light to kill harmful micro-organisms.

Table 1. INDIAN STANDARDS FOR DRINKING WATER  -  SPECIFICATION                   ( BIS  10500 : 1991 )

         Bacteriological standards

         Coliform count             0 in 100 ml of sample

         E.Coli count                  0 in 100 ml of sample