The Hindu Business Line : `Rainwater harvesting holds the key'

RAINWATER harvesting, if done by all, could be an ideal solution to the acute water scarcity, as it would help recharge the underground water table. In fact, it is the only source of natural water and during the rainy season a lot of water is wasted through surface flows to the sea.

Being a clean source of water, even through rooftop rainwater harvesting, this wastage can be reduced and that in turn would augment supply of potable water to people.

Speaking at a seminar recently, Mr M.P.S. Nair, an expert and former Chairman of Institution of Engineers India (IEI), said that in areas where there is inadequate groundwater supply or surface resources are either lacking or insufficient, rainwater harvesting offers an ideal solution.

Considering the increasing shortage of good quality water all throughout the year, the Centre has already directed the State Government to provide certain provisions in building rules, pertaining to incorporation of rooftop rainwater harvesting arrangements in building.

In this context, the Kerala Government has amended the Kerala Municipality Building Rules, 1999 necessitating all new building construction to incorporate rooftop rainwater harvesting systems in the design stage itself.

Besides, the National Building Code (NBC) also provides for rooftop rainwater harvesting for built-up area, said Mr Nair.

Rainwater harvesting is an appropriate option for augmenting groundwater storage in urban areas, where natural recharge has been considerably reduced due to increased urban activities and not much land is available for implementing any other artificial recharge measure, he added.

"It also helps in reducing flood hazards in urban areas where fast rate of urbanisation has reduced availability of open surfaces. It improves the quality of groundwater through dilution, especially for fluorides and nitrates."

The structures required for harvesting rainwater are simple, economical and eco-friendly.

In coastal areas over extraction of groundwater leads to saline water intrusion. Therefore, recharging the groundwater aquifer helps in arresting this intrusion.

Groundwater in many areas is either of poor quality or not is potable due to the presence of clay or anthropogenic pollutants. Recharge of groundwater using rainwater helps to improve the groundwater quality considerably.

"Buildings that are constructed on clay soil formations are prone to develop cracks during dry periods. As rainwater harvesting helps to sustain the moisture level in the sub-soil, such adverse conditions could be avoided."

In a normal year India gets one per cent of the total global rainfall on two per cent of the geographical area. Much of the water is wasted for want of adequate schemes for conservation and proper storage.

The annual per capita water availability in the country is estimated to be varying in the range of 300 to 13,754 cubic metres. The national average was 1,829 cubic metres in 2001 and is likely to decline to about 1,557 cubic metres by 2015 due to increase in population.

As per well-accepted criteria, any solution of water availability of less than 1,000 cubic metres per capita per year is considered as a scarcity condition. Accordingly, 47 per cent of the geographical area and 55 per cent of the population in the country will be under scarcity conditions by 2050, according to Mr Nair.

"To meet the water demands of the growing population, we may have to resort to non-conventional methods such as inter-basin transfers, artificial recharging of groundwater, desalination of seawater and so on."