Front and back of the earth
The blue area represents water
| Most of the earth consists of water, there is much more water than there is land. |
About 70% of the earth's surface is covered in water. But water also exists in the air as vapour and in aquifers in the soil, as groundwater.
The total water supply of the world is 1.400.000.000 km3. (A m3 of water equals 1,000 litres.)
Each year, 119.000 km3 of water precipitates on land and 74.200 km3 evaporates into the atmosphere, by evapotranspiration from soil and vegetation. On ocean and sea surface 450.000 km3 of water falls every year and 502.800 km3 evaporates.
Of the freshwater on Earth, about 2.200 km3 flows in the ground, mostly within half a mile from the surface. About 135.000 km3 of water can be found in the atmosphere as water vapour, in lakes, soil moisture, marshes and wetlands, rivers, plant and animals. Groundwater and fresh water stored in surface bodies and in the atmosphere represent an available resource of fresh water. Most of the freshwater is stored in glaciers and icecaps, mainly in the Polar Regions and in Greenland, and it is unavailable. This is another 24.500.000 km3 of water, formig the 69.5 % of the total fresh water of the Earth.
As oceans are very wide and there are multiple to be found on earth, oceans store most of the earth's water. This is apparently 97% of the total amount of water on earth, 2% of which is frozen.
Of all the water on earth, which is 97,14% of the total amount of surface water, only 2,59% is freshwater. Of this 2,59% another percentage is trapped in ice caps and glaciers, which is about 2%. The rest of the freshwater is either groundwater (0,592%), or readily accessible water in lakes, streams, rivers, etc. (0,014%)
| || From the quantities that came up in the questions listed above, one can conclude that less than 1% of the water supply on earth can be used as drinking water. |
Humans mainly consist of water; it is in all our organs and in is transported throughout our body to assist physical functions. When a human does not absorb enough water, dehydration is the result. This is not very surprising, given that 66% of the human body consists of water.
There are four different causes of water scarcity: a dry climate, drought (a period in which rainfall is much lower and evaporation is higher than normal), drying of the soil due to activities such as deforestation and overgrazing by livestock and water stress due to increasing numbers of people that rely on limited levels of run-off.
There are five ways to increase water supplies in a particular area: build dams and reservoirs to store run-off, bring in surface water from another area, withdraw groundwater, convert salt water to freshwater (desalination) and improve the efficiency of water use. These methods all have their pros and cons.
| Flooding means that there is too much water, so that it will end up in places where we do not want it to be, such as rural areas. |
Natural flooding by streams is the most common type of flooding and is primarily caused by heavy rainfall or rapid melting of snow. It causes water in the stream to overflow its normal channel and to cover the neighbouring area. Areas that are expected to flood once in a while are called flood planes. People have settled on flood planes since the beginning of agriculture, because the soil is fertile and the water is readily available for watering of crops. Communities can use the water for transport and flood planes are suitable for buildings, highways and railroads, because they are flat. People may decide that these benefits outweigh the risk of living on a flood plane.
We surround the flood planes with safety measures such as dikes, but we have seen in the past that these measures are not always satisfactory.
On marine coasts flooding most often results from storms and cyclones, which cause waves of up to 30 meters high.
Floods can be beneficial, because they provide the world's richest farmland as they leave behind a cover of nutrient-rich silt on the soil. Floods also recharge groundwater and fill up wetlands, so that the ecosystems there will be sustained.
Off course most people see floods as a threat to their homes and families, but for the larger parts of those disasters we only have ourselves to blame. The number of floodings is increased by human activities such as removing and replacing vegetation, which causes that less water can infiltrate into the ground and all rainwater floods to the lakes and streams. Other human activities that can cause flooding are: overgrazing by livestock, forest fires, mining activities and urbanization.
Each year flooding kills thousands of people and causes tens of billions of dollars in property damage.
For more specific questions on water quantities, move to our specific water quantity questions
For water terminology check out our Water Glossary or go back to water FAQ overview
Feel free to contact us if you have any other questions also on the cost of water