Sri Lanka, Sept. 25 -- Rainwater harvesting is the practice of collecting the rain that falls on your roof, storing it in a covered tank or drum, and using it later. In Sri Lanka, it can cut water bills, help households through dry spells, and ease pressure on drains. A single 100 m2 roof collects about 2,000 litres from one heavy shower.

The timing matters this year. As of September 19, drought has affected 169,071 people from 51,959 families across 10 districts, according to the Disaster Management Centre (DMC). Monaragala is the worst hit, with more than 42,000 people affected, and water bowsers are now supplying over 142,000 people.

The Meteorology Department puts the chance of a strong El Nino developing between October and Decemb...