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Specific questions on water quantities

Specific questions on water use and the amounts of available water on earth

1. How much water is available on earth and how much of this water is available for humans?

Approximately 1385 million cubic kilometres of water are available on earth. 97,5% of the water is salt water that can be found mainly in oceans. Only 2,5% is freshwater that can be used by plants, animals and humans. However, nearly 90% of this freshwater is not readily available, because it is centred in icecaps of the Antarctic. Only 0.26% of the water on this world is available for humans and other organisms, this is about 93.000 cubic kilometres. Only 0.014% of this water can be used for drinking water production, as most of it is stored in clouds or in the ground.

2. How much freshwater will be available for one person?

Increases in world population means increased water use and less availability on a per capita basis. In 1989 there was some 9,000 cubic metres of freshwater per person available for human use. By 2000, this had dropped to 7,800 cubic metres and it is expected to plummet to 5,100 cubic metres per person by 2025, when the global population is projected to reach 8 billion.

3. What is the total world annual consumption of potable water and seawater?

People already use over half the world's accessible freshwater now, and may use nearly three-quarters by 2025. Over the twentieth century, the world annual water use has grown from about 300 km3 to about 2,100 km3 (see chart).

In this chart the annual water consumption is shown, as withdrawal and use. These two concepts are separated, because much of the withdrawn water is later returned to the water cycle, after application. An example is cooling water; it is used for power generation and is immediately released for further use downstream.

Each country has a different equivalent use per person.

The annual per capita water use for each part of the world:
- North Americans use 1,280 cubic meters
- Europeans and Australians use 694 cubic meters
- Asians use 535 cubic meters
- South Americans use 311 cubic meters
- Africans use 186 cubic meters

Water is used for three main purposes; agricultural uses, industrial uses and domestic uses. Each country uses a different amount of its available water for these three main purposes. In percentages, the global use for the three main purposes is divided up as follows:

- Agriculture (mostly irrigation) = 69 %
- Industry = 23 %
- Domestic use (household water = drinking water, sanitation) = 8 %

Current global water withdrawals for irrigation are estimated at about 2,000 to 2,555 cubic kilometres per year. The annual water volume used by industry is estimated 975 km3.

The water that humans use for drinking water preparation is mainly freshwater. But freshwater availability has become a problem over the years, as only 0.014% of the water on earth is readily available freshwater for drinking purposes. In some countries they are trying to solve this problem by withdrawal and desalination of seawater. Right now, 0.1% of the water that is used by humans is desalinated seawater.

4. What are the projected needs for water in the next 10 to 50 years?

Global consumption of water is doubling every 20 years, more that twice the rate of human population growth. According to the various water research agencies, the world water use is expected to triple in the next 50 years.
Almost half of the world's population lives in 263 international river basins, but two-thirds of these basins have no treaties to share water. Because of this, wars over water are extremely likely to happen in the future, when water becomes scarcer. Disputes could also consist over aquifers in time.

The world's population of six billion people is already using about 54 per cent of all the accessible freshwater found in rivers, lakes and underground aquifers. By 2025 the human share will be 70 percent, based on the population increase. If per capita consumption of water resources continues to rise at its current rate, humankind could be using over 90 per cent of all available freshwater within 25 years.

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

Water scarcity is caused by dry climates, drought, desiccation, or water stress. Water scarcity caused by drought has killed over 24,000 people a year since the 1970's. Over 40% of the world's population now experiences water shortages that threaten their agriculture and industry and also their personal health. Today over a billion people do not have access to clean drinking water and by 2025 at least 3 billion people in 90 different countries are expected to face severe water stress. The main problem that causes this is not a shortage of water, but the wasteful and unsustainable use of available water supplies.

6. What is the average cost of water per cubic meter in different countries?

The costs of a cubic meter of water are known to differ between countries. In this chart, the costs of one cubic meter of water are shown, for 14 different countries.



7. How much does a cubic meter of desalinated water cost in various countries?

When water is desalinated through the Reverse Osmosis (RO) treatment, the costs are as follows:
Depending on the site of the plant, total costs of desalinated seawater vary between 0.5 and 0.8 dollars/ cubic meter. This makes desalinated water a more expensive resource than freshwater for many countries, but it is definitely not an unnecessary resource.
It has to be noted that the above-mentioned costs do not include distribution towards points of use (houses, factories, etc.).

8. What will happen to the cost of desalinated water in the next 10 to 50 years?

The costs should decline within the next 10-50 years, as membranes become cheaper and more efficient. However, the costs are mostly energy related, so the energy use should be taken into account.

9. How will population increases influence water use?

Global population now exceeds 6.2 billion, more that double what it was in 1950, and is currently projected to rise to between 7.9 billion and 10.9 billion by 2050. Even when the population does not increase, water use will still grow. A population increase will only make the global water use rise faster.

An important issue here is that the water of our world is not divided up fairly between all its inhabitants. Water shortages are most likely to occur in developing countries, which have the highest population rates. In the developed world the per capita use is much higher than the projected need. The people in developed countries that use too much water tend to blame people in developing countries, because developing countries experience the largest population growth. But in developing countries, over a billion people have no excess to clean drinking water.

Resources:

http://www.gvrd.bc.ca/sustainability/greeninfrastructure/CostofWater.pdf
http://www.newscientist.com
http://www.ees.ufl.edu
http://www.wwfpak.org/water/water.htm

Living in the Environment, a book by G. Tyler Miller Jr.
State of the world 2003, a book by Cris Bright and others
Water, a natural history, a book by Alice Outwater
The Sceptical Environmentalist, a book by Matt Ridley

For more answers to your questions on water quantities, move to our Water Quantity FAQ

For the answers to your questions on drinking water, move to our Drinking Water FAQ

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