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World Demand for Water







How much water do humans use? The answer depends on where they live and on their socioeconomic status. Under primitive conditions a person will consume three to five gallons per day for drinking and subsistence farming. In a city where water is also used for cleaning, manufacturing, and sanitation, per capita use is around 150 gallons per day. In the United States, which has among the highest water consumption rates in the world, each person uses an average of 1,340 gallons of water per day.

Item
Gallons used
1 pound of steel
25
1 gallon of gasoline
10
1 load of laundry
60
1 ten-minute shower
25-50
1 pound of cotton
2,000
1 pound of grain-fed beef
800
1 loaf of bread
150
1 car
100,000
1 kilowatt hour of electricity
25
1 pound of rubber
100


Water resources are not distributed evenly in space or time around the world. Global circulation patterns create wet and dry climate zones, and in some regions seasonal or multi-annual climate cycles generate distinct wet and dry phases. As a result, some regions have larger freshwater endowments than others.



Although developed nations generally have more water available than many countries in Africa and the Middle East, some areas with good water endowments still are subject to "water stress" because they are withdrawing water from available supplies at extremely high rates. High-intensity water uses in industrialized nations include agricultural production and electric power generation, which requires large quantities of water for cooling. In the United States electric power production accounts for 39 percent of all freshwater withdrawals, although almost all of this water is immediately returned to the rivers from which it is withdrawn. Agriculture consumes much more water because irrigation increases transpiration to the atmosphere.

As of 2002, 1.1 billion people around the world (17 percent of global population) did not have access to safe drinking water and 2.6 billion people (42 percent of global population) lived without adequate sanitation. As a result, millions of people die each year of preventable water-related diseases. Most of the countries with inadequate supplies of safe drinking water are located in Africa, Asia, and the Pacific, but problems persist elsewhere as well. For example, many households lack adequate sewage treatment services in Eastern Europe. And inequity among water users is widespread: cities often receive better service than rural areas, and many poor communities in both rural and urban areas lack clean water and sanitation.
  
 


Although these challenges apply in many regions, it is hard to make broad generalizations about water resources at the global or national level; to paraphrase the famous saying about politics, all hydrology is local. The basic geologic unit that scientists focus on to characterize an area's water supply and water quality with precision is the watershed or catchment area—an area of land that drains all streams and rainfall to a common outlet such as a bay or river delta. Large watersheds, such as the Amazon, the Mississippi, and the Congo contain many smaller sub-basins.
 


  Mississippi River


Amazon River

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