Precious fluid

Nov. 11: Artificial recharge of water through rooftop rainwater harvesting can be an ideal option to reduce water scarcity as well as pollution in the city.

This was stated in a recent report published by Central Ground Water Board, which said rainwater harvesting by such means might be considered the most viable means to augment water supply for domestic needs, as incidence of rainfall was high in the area.

“The city is bestowed with good rainfall which is more than 1,700mm at an annual average. This rainfall can be harnessed and stored in surface or sub-surface storage tanks. Individual houses, school buildings and offices may be used for rooftop rainwater harvesting,” the report added.

On an average, a house with 100 square metre of roof and 1.7mm rainfall can harvest about 1,36,000 litres of water per annum. The average cost of a rooftop rainwater harvesting structure is about 2 to 3 lakh, including the storage tank.

Water supply in the city is dependent on both surface and ground water. A major part of the water supply (72,000 cubic metre per day) by Guwahati Municipal Corporation (GMC) within the municipality area comes from the Brahmaputra. The Assam Urban Water Supply and Sewerage Board also supplies 9,000 cubic metre per day of river water.

Besides, NF Railway and Indian Oil Corporation have their own water supply systems, supplying 6,000 and 11,000 cubic metre per day respectively from the Brahmaputra.

However, a major part of the population is dependent on ground water through individual dug wells, shallow tube wells and deep tube wells.

The public health engineering department supplies water to a considerable percentage of population through deep tube wells and spring sources.

“In hilly parts, artificial recharge may be done by constructing subsurface dykes at suitable locations to arrest natural discharge and augment the natural infiltration process. Like in many cities of India, rooftop rainwater harvesting should be made mandatory for every house,” the report said.

It said over the last decade, the city had experienced an unprecedented population growth of 154 per cent. Resultant developmental activities have led to filling up of marshes and conversion of agricultural low lands to residential or commercial plots.

The report said waterlogging, pollution from sewage and garbage dumping, unplanned ground water abstraction, high iron content in ground water and sporadic high fluoride content are the major ground water-related problems in the city.