India is deep in Asia\u2019s $4 trillion water risk. That\u2019s how much GDP is at stake if the region cannot better manage rivers that its economies depend on, according to China Water Risk. India looks most exposed. It\u2019s one of 16 countries that rely on a network of waterways flowing from the Himalayas. That\u2019s a problem: its glaciers are melting fast due to climate change, altering the volume and reliability of river water. Meanwhile regional populations and economies are growing, driving demand for water. And most of the basins cross international borders, complicating management of a dwindling resource. India already suffers from water scarcity, exacerbated by recent low rainfall \u2013 last month was the driest October on record for 42 years. Shortages in the capital, New Delhi, have led to tussles, and even killings. With current patterns, demand for water is expected to be twice available supply by 2030 according to McKinsey and the Water Resources Group, as the economy is set to double in size, reckons PwC. Meanwhile, almost 70 percent of the country\u2019s water is contaminated, according to Niti Aayog, a government think tank. Urban residents report waterways choked with excrement and plastic. Read Also| G20 Summit: Yoga bridging the vast distance between India, Argentina, says PM Narendra Modi The Indus and Ganges watersheds account for around $1 trillion in GDP and are home to around half India\u2019s 1.3 billion population. Water stress threatens guzzlers like agriculture, which uses most of India\u2019s water. It also endangers the electricity supply, much of which is dependent on water-cooled thermal generators. China, meanwhile, is tackling its own severe water stress head-on. Beijing integrated water management into its five-year plans, capping consumption and assigning responsibility for tracts of water to individual officials. Private-sector quotas have been introduced, and there is a robust trade in water credits on Taobao, China\u2019s eBay, according to CWR founder Debra Tan. But India is different. Individual states covet control over resources; national and provincial borders split rivers, entangling multiple interests; and the thirsty agricultural sector is powerful. Efforts to coordinate from the centre have fallen flat: A 2016 draft bill aimed at tightening up controls languished, while a campaign to clean the Ganges faltered. Other countries that are irrigating growth with Himalayan water face similar challenges \u2013 notably Vietnam, Cambodia, Thailand and Myanmar. A literal liquidity crunch is coming down the mountain.