The world is facing a real crisis in obtaining fresh water. This topic, central to any Population Nutrition economy has been discussed at length in a recent edition of Nature
1 billion people lack access to fresh drinkable water.
2 billion lack proper sanitation.
Whilst climate change is an important factor other factors are contributing to the problem. Growing populations and increasing energy requirements. India and China are prospering and consuming more meat. It takes 15,500 litres of water to produce 1 kilogram of beef. Which is 10 times the amount of water to produce 1 kg of wheat.
Cooling electricity plants requires fresh water, the United States uses more than 500 billion litres of fresh water a day to cool its power stations. Australia is struggling to obtain sufficient water to grow wheat.
Energy usage is increasing and the use of water will double.
To produce sufficient food we will need 12,000 cubic km of water , equal to the
Many of the world’s rivers are drying. volume of Lake Superior every year.
There is a need to use what is called blue water efficiently , rivers, lakes, reservoirs and underground aqueducts but also green water that is rain water.
Green water conservation means changes in agricultural techniques to ensure that rain is effectively used. Which is not universally the case currently
Desalination is an attractive option but is very energy costly. Polyamide membranes and reverse osmosis plants are more efficient than thermal distillation plants. At the present time 40 million cubic metres of water is produced a day world wide. The average cost is 3.5 times the cost of pumping from aquifer, though this varies with the locality. . Fouling of the filters is a real problem and costly.

Editorial Nature 2008, a fresh approach to water Nature vol 452 pp 254
Schiermeier 208 Purification with a pinch of salt Nature vol 452, pp 260-61
Water under pressure a News Feature 2008 Nature vol452. pp 269-316

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