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13.12: Water Distribution

Difficulty Level: At Grade Created by: CK-12
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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.

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. In 1995, about 40% of the world’s population faced water scarcity (Figure below). Scientists estimate that by the year 2025, nearly half of the world’s people won’t have enough water to meet their daily needs. 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.

Water supply compared to population.


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. 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/.

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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Difficulty Level:
At Grade
Date Created:
Feb 24, 2012
Last Modified:
Dec 15, 2016
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