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of temporary storage, such as a reservoir; a means of transporting water from storage to the treatment plant such as pipes or aqueducts; treatment facilities for improving water quality; and more pipes
to carry the cleaned water to its consumers. In most cases the used water is then returned to a river after first being cleaned in a treatment plant.
Water supply is extremely important to all countries, and large amounts of money are spent on getting clean water to all homes. However, not all countries have enough money for this, and many people in the developing world still get their water directly from rivers. As a result, they suffer many more diseases than people in wealthy countries. (See also: Desalinization and Irrigation.)
Water table
The natural level of water in a soil or rock. Below the water table the soil or rock is saturated.
When a water table rises to meet the surface of the land, water seeps out of the ground, often as a spring. The headwaters of many rivers have formed this way.
 Water table—The water table is the upper surface of waterlogged ground.
Well
 Well—A well is sunk to the level
of the permanent water table in an underground aquifer.
Spring
Water vapor
(See: Vapor.)
Well
A vertical shaft that is drilled down into an aquifer in order to obtain
The height of a water table is very important for people who rely on wells for their water. The water table rises and falls each year, so the depth of water in the well also rises and falls. If the well is not deep enough, the falling level in summer can leave the well dry. Some wells need to be over 100m deep to keep them from running dry in summer.
Spring
water for drinking and other home uses, for industry, or for farming.
A small well, meant to serve
a single house, may be about 1m across and lined with brick. The wells needed to supply water to a city are on an altogether different scale. These wells are often sunk many tens of meters down into a large, reliable aquifer. They are not open wells, but enclosed, and are drained by pipes about 30cm across. These wells are sealed so that the clean water coming from the well is not contaminated from the surface. The water in these wells is often pumped out of the aquifer with motorized pumps. (See also: Groundwater.)
Wetlands
Areas containing shallow water or saturated soil, where dead plant matter rots slowly, and plants are adapted to wet conditions.
Wetlands include swamps, bogs, marshes, mires, tundra, and fens. They cover about 5% of the land surface of the world.
Rice paddies are artificial wetlands covering about 1 to 2% of the land surface. Half the world’s population gets its staple food from these rice paddies.
Water table
Water table
Wetlands
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