Indication whether the existing water supply is sufficient or not, the per capita supply can be regarded as though seems to be freshwater available worldwide in sufficient quantities at first glance, there are significant and sometimes dramatic differences in single regions due to the spatial and temporal variation of precipitation. Experts expect an increasing number of countries in which a requirement in question is due to increasing scarcity of per head supply of renewable resources. (See Federal Ministry for economic cooperation and development, no. 94 materials): of the total occurring on Earth water 97.5 percent sea or brackish water and only about 2.5 percent is freshwater. The far majority of fresh water in ice sheets and glaciers is bound with 69 percent.
About 30 percent of fresh water are clean water and only a vanishingly small part of 0.98 percent as surface water drains. If as a result of the greenhouse effect the Earth’s temperature increases, which has probably an increased evaporation and consequently a higher precipitation and discharge to the result. The level of knowledge about the respective water resources is the basis for sustainable management, as well as an important prerequisite to the possibilities for the development of water resources under technical, to be able to assess the economic and environmental point of view. As a criterion for the assessment of the water supply, so the per capita supply can vary from 500 m3 per year (in the Sahel countries) up to more than 100,000 m3 per capita per year (Canada). A supply of less than 500 m3 per capita per year is seen as a critical lower limit an annual yield of less than 1,000 m3 per capita as very low and an annual yield of less than 2,000 m3 as critical. Gem. an evaluation of the BMZ a total of 15 countries have an annual per capita supply of below 500 m3, 12 countries this value is between 500 and 1,000 m3, other 22 countries have a per capita supply between 1,000 and 2,000 m3 (water-stressed-countries”). see, in addition such as Jorg Becker: location indicators I.
performance levels on the spot, sensors on the pulse location, ISBN 978-3-8391-1823-8 or Jorg Becker: site analysis from the cockpit of the indicators visiting the counter area, ISBN 978-3-8423-1858-8. Worldwide, agriculture with currently 68 percent of the collection is the largest consumer of water. Although the total amount of water for agriculture will increase, the agricultural water withdrawal at the global water extraction will decline, because the water is drawn by the industry as likely triple. The water is drawn by the households is strongly increasing mainly in Africa and Asia, in Europe and South America, however, be some more down. The proportion of households worldwide is 8 percent of the total use. Depending on the economic structure and technology, the share of developing countries on industrial water use is between 10 and 30 percent, compared with a share of 60 to 80 percent in developed countries.