'The real threat to our future is peak water'

As population rises, overpumping means some nations have reached peak water, which threatens food supply, says Lester Brown Kansas's Quivira National Wildlife Refuge in 2012, during the worst drought in the United States in more than 50 years. Photograph: Jim Reed/Corbis Peak oil has generated headlines in recent years, but the real threat to our future is peak water. There are substitutes for oil, but not for water. We can produce food without oil, but not without water. We drink on average four quarts (4.5 litres) of water per day, in one form or another, but the food we eat each day requires 2,000 quarts of water to produce, or 500 times as much. Getting enough water to drink is...