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withdrawn.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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