Today a third of humanity is suffering from water scarcity. Specialists use the term “water stress” when the demand for water exceeds the available freshwater supply by 10%. Although of a renewable resource may not seem like much, we should not forget that before mankind’s intervention, 100% of this was used by ecosystems. This extra demand is enough to dry a watercourse, drain a spring, or prevent the replenishment of groundwater.
While the populations of Canada and the Amazon or Congo basin have a plentiful water supply, the people of the Mediterranean basin, Central Asia and Mexico are at greater risk of scarcity. The particular problem with water is that it is difficult to transport in large quantities over great distances.
One solution is to use the same water several times. An increasing number of industries are reusing water, retreating it up to 30 times in some cases. Domestic wastewater, known as “greywater,” can be reused to water a garden or flush a toilet, reserving drinkable water for human consumption, cooking, or washing. In countries where water is scarce, wastewater from cities is retreated for use in agriculture. In Israel, for example, 10% where the average rainfall is 1 inch (250 mm) a year, 70% of wastewater is recycled, allowing 49,000 acres (20,000 hectares) water of land to be watered.
There are many other ways of saving water, especially by being aware of how much of it we consume. Some of this water is invisible: it is used to make a product, but is not present in the product itself. This is called virtual water. One pound of grain means hundreds of gallons of irrigation water; a pair of cotton jeans require 2,860 gallons (10,850 liters) of water; a cup of coffee 9 gallons (35 liters); a sheet of paper 2.5 gallons (10 liters). A single tomato contains 3.5 gallons (13 liters) of virtual water, which is more than many people use in a day. Paradoxically, some countries that face water scarcity are actually exporting some of their limited water resources in the form of agricultural or manufactured products.