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Rainwater Harvesting Benchmarks to Address South Asia’s Urban Water Crisis
Carefully designed rainwater harvesting systems can reduce water stress and help in the management of water crises in major South Asian cities, home to about a quarter of a billion people. A straightforward formula is provided here for calculating rainwater harvesting targets in major South Asian cities. Modest achievements in rainwater harvesting can dramatically mitigate the water crisis for urban inhabitants of this region, requiring fairly inexpensive modes if relevant projects are meticulously planned and implemented.
Water scarcity has reached worrisome levels in many parts of the world. The United Nations (UN) defines absolute water scarcity for countries with less than 1,400 litres/day/person. UN estimates based on this threshold suggest that about two billion people may be living in countries that are experiencing acute water stress. Additionally, about 700 million people worldwide are facing the risk of getting displaced due to intense water scarcity by 2030. The breadth and intensity of this civilisational crisis are truly breathtaking. To complicate things further, our ability to confront the challenges is also shrinking rapidly because about a third of our world’s largest groundwater systems are distressed due to over-harvesting.
The World Health Organization (WHO) is also very concerned about water scarcity. Life as we know it crucially depends on the availability of safe, clean, and continuously available water supply. Thus, some of the oldest civilisations flourished on the banks of large rivers like the Indus and the Nile. Safe potable water is essential to meet “basic human needs,” defined as the “quantity of water needed to meet basic hygiene needs and ensure basic food hygiene.” The WHO recommends at least 20 litres/day/person to meet basic human needs. Arguably, this requirement is also expected to vary depending on particular weather and geography. For example, the requirements may be higher in arid and semi-arid regions, especially during the summer months.
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