Global population, economic development and a growing appetite for meat, dairy and fish protein have raised human water demand sixfold in 50 years. Meanwhile, supplies have been diminished in several ways: an estimated 845,000 dams block most of the world's rivers, depriving downstream communities of water and sediment, and increasing evaporation; up to half of water is lost in leakage; another 1bn people simply have no proper infrastructure; and the water left is often polluted by chemicals and heavy metals from farms and industry, blamed by the UN for poisoning more than 100m people. And still the rains are getting less reliable in many areas.
Underlying these problems is a paradox. Because water, and the movement of water, is essential for life, and central to many religions, it is traditionally regarded as a 'common' good. But no individuals are responsible for it. From Wadi Esseir to the arid American Midwest, farmers either do not pay for water or pay a fraction of what homeowners pay, so they have less incentive to conserve it and might deprive suppliers of funds to improve infrastructure.