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Water Distribution

The unequal distribution of water around the world is one of the causes of water scarcity.

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Water Distribution

Will water cause the next war?

Wars have been fought over oil, but many people predict that the next war will be fought over water. Certainly, water is becoming scarcer.

Water Distribution

Water is unevenly distributed around the world. Large portions of the world, such as much of northern Africa, receive very little water relative to their population (Figure below). The map shows the relationship between water supply and population by river basin.

Blue means there is a lot of river water for each person who lives in the river basin. Salmon pink means there is very little river water for each person who lives in the river basin.

For many people in industrialized countries, getting water is as easy as turning on a faucet, and it's rather inexpensive. But freshwater isn't evenly distributed throughout the world. More than half of the world's water supply is contained in just six countries: Brazil (which significantly outstrips other countries), Canada, Russia, Indonesia, China, and the United States - with China consuming the greatest amount of fresh water.  Urban areas, obviously, have a greater need for water beyond the basics for drinking and sanitation. But overpopulation in undeveloped countries means that many people don't even get the basics.

Over time, there will be less water per person within many river basins as the population grows and global temperatures increase so that some water sources are lost. In 2025, many nations, even developed nations, are projected to have less water per person than now (Figure below).

The same map but projected into 2025.

Water Shortages

Water scarcity is a problem now and will become an even larger problem in the future as water sources are reduced or polluted and population grows. As of 2013, some 1.2 billion people - almost one fifth of the world - live in areas of physical water scarcity, while another 1.6 billion face what can be called economic water shortage.  The situation is only expected to worsen as population growth, climate change, investment and management shortfalls, and inefficient use of existing resources restrict the amount of water available to people.  It is estimated that by 2025 fully 1.8 billion people will live in countries or regions with absolute water scarcity, with almost half of the world living in conditions of water stress.  Nearly one-quarter of the world's people will have less than 500 m3 of water to use in an entire year.  That amount is less water in a year than some people in the United States use in one day.  

According to the United Nations, an area is said to be experiencing water stress when annual water supplies fall below 1,700 cubic meters per person. A region is said to face water scarcity when supplies fall below 1,000 cubic meters per person, and absolute water scarcity is when supplies drop below 500 cubic meters a year (Table 1 below).

License: CC BY-NC 3.0


With water use increasing every year, many regions in the United States are even starting to feel the pressure. In the last five years, nearly every region of the country has experienced water shortages. At least 36 states are anticipating local, regional, or statewide water shortages in 2013, even under non-drought conditions.


Droughts occur when a region experiences unusually low precipitation for months or years (Figure below). Periods of drought may create or worsen water shortages.

Human activities can contribute to the frequency and duration of droughts. For example, deforestation keeps trees from returning water to the atmosphere by transpiration; part of the water cycle becomes broken. Because it is difficult to predict when droughts will happen, it is difficult for countries to predict how serious water shortages will be each year.

Extended periods with lower than normal rainfall cause droughts.

Effect of Changing Climate

Global warming will change patterns of rainfall and water distribution. As the Earth warms, regions that currently receive an adequate supply of rain may shift. Regions that rely on snowmelt may find that there is less snow and the melt comes earlier and faster in the spring, causing the water to run off and not be available through the dry summers. A change in temperature and precipitation would completely change the types of plants and animals that can live successfully in that region.

Water Scarcity

Water scarcity can have dire consequences for the people, the economy, and the environment. Without adequate water, crops and livestock dwindle and people go hungry. Industry, construction, and economic development is halted, causing a nation to sink further into poverty. The risk of regional conflicts over scarce water resources rises. People die from diseases, thirst, or even in war over scarce resources.

California's population is growing by hundreds of thousands of people a year, but much of the state receives as much annual rainfall as Morocco (approximately 346 mm/year). With fish populations crashing, global warming, and the demands of the country's largest agricultural industry, the pressures on our water supply are increasing.

Find out more at http://science.kqed.org/quest/video/state-of-thirst-californias-water-future/.

Many of the world’s most important food-producing regions depend on freshwater from massive underground aquifers that have built up over thousands of years.  The Ogallala Aquifer in the midwestern United States.  The Upper Ganges, sustaining India and Pakistan.

License: CC BY-NC 3.0

Going, going… gone? (Kevin Clark-AP) [Figure2]

Yet many of those aquifers are now being sucked dry by irrigation and other uses faster than they can be replenished by rainwater (Figure above).  It’s unclear when many of these aquifers will be completely emptied — scientists are still trying to measure how much “fossil water” these aquifers actually hold.  But it’s a worrisome trend: About 1.7 billion people rely on aquifers that are rapidly being depleted.  And once they’re gone, it would take thousands of years to refill them.

Some aquifers receive more rain than is being used up by humans.  The Floridian Aquifer in the southeastern United States, for instance, can get quickly refilled by a big storm (though it still faces problems with saltwater contamination and overuse).  Russia has plenty of freshwater.  But all too often, irrigation and drinking water use is drawing out more water from the aquifers than the rain can refill.

License: CC BY-NC 3.0

The map compares the usage footprint with the actual rainfall a particular aquifer gets. Blue areas receive more rain than is being used up by humans. Orange or red areas indicate places where irrigation and drinking water use is drawing out more water from the aquifers than the rain can refill. [Figure3]

In some areas, the imbalance is staggering.  Take, for instance, the Upper Ganges in northern India, which sustains farm irrigation in both India and Pakistan.  The underground reservoir there would essentially need 54 times as much rain as it currently gets to replenish the water that’s being used by farmers and the local population.  In the United States, aquifers are taking on increasing importance as food production expands and drought becomes a nagging issue.  In regions like western Kansas, where farmers don’t get enough rain for their crops, they depend on irrigation, using freshwater from one of the world's largest aquifers - the Ogallala Aquifer.

About 27 percent of U.S. irrigated farmland depends on the Ogallala aquifer, and it’s a key region for livestock, corn, wheat, and soy.  But it’s slowly getting depleted.  Follow the link to see a table showing the High Plains (Ogallala) Aquifer Water-Level Monitoring Study between 1987 and 2011 from USGS.  In some Kansas counties, the water table is dropping by as much as two feet per year.  And, as David Biello notes, once the Ogallala gets drained, it would take about 6,000 years to recharge with rainfall.

Click here to see more details concerning the Ogallala Aquifer.

Conflicts Over Water

As water supplies become scarce, conflicts will arise between the individuals or nations that have enough clean water and those that do not (Figure below). Some of today’s greatest tensions are happening in places where water is scarce. Water disputes may add to tensions between countries where differing national interests and withdrawal rights have been in conflict. Just as with energy resources today, wars may erupt over water.

By 2025, many nations will face water scarcity. For the nations in red, there will simply not be enough fresh water; the nations in brown may not be able to afford to supply their citizens with fresh water.

Water disputes are happening along 260 different river systems that cross national boundaries. Some of these disputes are potentially very serious. International water laws, such as the Helsinki Rules, help interpret water rights among countries.


  • A lot of the problem with water is that it is not evenly distributed across the planet.
  • Many of the world's people live with water scarcity, and that percentage will increase as populations increase and climate changes.
  • Some people predict that, just as wars are fought over energy now, future wars will be fought over water.


Use this resource to answer the questions that follow.


1. What is water scarcity?

2. Why do people take water for granted?

3. How much freshwater is there on Earth?

4. How many people do not have access to clean water?

5. What will occur by 2025?

6. What is physical water scarcity? Where does this occur?

7. What is economic water scarcity? Where does this occur?


1. How will changing climate affect the availability and distribution of water?

2. How do human activities affect the occurrence of droughts?

3. How do so many people live with so little water?

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  1. [1]^ License: CC BY-NC 3.0
  2. [2]^ License: CC BY-NC 3.0
  3. [3]^ License: CC BY-NC 3.0

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