The Guwahati Municipal Corporation (GMC) has done well by issuing an order making it mandatory for all commercial, residential, educational and industrial buildings in Guwahati to implement rainwater harvesting systems with immediate effect. A decision that should have been taken at least ten years ago, rainwater harvesting can help ease two major problems of Guwahati. First and foremost, since the government water supply hardly covers 30 per cent of the city’s households, rainwater harvesting will help citizens collect and store their own water coming down as rain. And secondly, it will reduce water run-off during rains to some extent and thus reduce urban floods to some extent. Experts say if there is 25 mm of rainfall in a certain area in a single day, a house having a rooftop spanning 100 sq.… metres or 1000 sq. feet can collect at least 2,000 litres of water through rainwater harvesting. This is enough to cover the water requirement of a household of six persons for three days. At present, a sizable section of residents of Guwahati have been buying water on a daily basis, especially in those areas where several high-rise apartment buildings coming up in a locality have sucked the ground water dry through large boring pumps. That most such water supplied is collected from doubtful and unsafe sources is another matter that requires close investigation by the concerned agencies. Moreover, apartment buildings cover the land, which prevents rainwater from naturally soaking into the ground. This, on one hand, causes depletion in groundwater level. On the other hand, the runoff enters drains or low-lying areas, thus heightening the risk of flood. A proper rainwater harvesting system in which rainwater is also collected in large storage tanks, on one hand helps replenish groundwater and reduces runoff, and on the other hand helps collect water for free. Rainwater, in its natural state, is considered relatively pure because it’s formed through evaporation and condensation, leaving behind impurities and salts on the earth’s surface. In contrast, groundwater, particularly in Guwahati and Assam, has a high degree of fluoride and arsenic content. Rainwater too can become contaminated while passing through the atmosphere in a polluted area, as also during collection. Despite that, experts claim that rainwater is better any given day. It is important to note that the Guwahati Building Construction (Regulations) Bylaws, 2014, and the Assam Unified Building Construction (Regulation) Bylaws, 2022, make it mandatory for all commercial, residential, educational, and industrial buildings in Guwahati to implement rainwater harvesting systems. Even otherwise, a normal household can easily harvest 500 litres of rainwater on a rainy day by organizing two plastic drums. Important to note, while the World Health Organisation (WHO) recommends 50 litres of water as the minimum requirement of a person per day, the Ministry of Housing and Urban Affairs suggests 135 liters per capita per day as a benchmark for urban residents of India.