It might, she argues, be difficult to use much more. Most land suitable for rain-fed agriculture is already being used. Water is life's bottom line. Humans are just bags of water. A man weighing 70kg will contain 43 litres of water, and even in a mild climate he will lose 2.5 litres a day by respiration, perspiration and urination.
Water is also, in effect, food.
Every eight seconds a child dies of a water-borne disease. Paradoxically a clean water supply is the most powerful single force in public health. Right now, according to the World Water Forum experts, 1bn people go without safe clean water, and 3bn go without adequate sanitation. But over the next 25 years almost 3bn people will be short of water. In 10 or 15 years, Gorbachev warned the forum, there could be war in the Middle East over water.