As cities around the world struggle to address water shortages, Dhaka, Bangladesh, is poised to become one of most populous cities in the world that requires new buildings to collect rainwater on their roofs. Rainwater harvesting is an old idea, but laws requiring the practice in urban areas are only starting to become mainstream. Bangalore, India already requires privately owned buildings to collect rainwater, and in western states in the U.S. are beginning to relax rules that make it illegal.[?] In Dhaka, the city is planning on modifying its building code by the end of this year to make the change.
Why it’s a good idea. Growing cities are straining water resources and droughts can shut off water across a city, yet rainwater in urban areas can be a burden, rather than a boon. Floods of storm water run-off can overwhelm sewer systems, change the flow patterns of surface water, and impact animals and plants in the surrounding area. Meanwhile, Dhaka’s population—more than 15 million people—requires 2.4 billion liters of water a day, but the city can only produce 2.1 billion liters. Stored rainwater can provide an alternative to polluted rivers and dwindling groundwater supplies for drinking.