Page 16 - Curriculum Visions Dynamic Book. To close the book, close the tab.

Drinking water
Drinking water
Water that is safe to drink. Very strict regulations are in place
in many countries to make sure that drinking water is of the highest quality and does not contain poisonous substances, pieces of soil, or disease-carrying organisms.
Drinking water has to be both clarified (made to look clean) and purified (disinfected) by the time it reaches taps. This is a complicated and expensive process. (See also: Aquifer; Aqueduct; Clean water; Reservoir; Water supply.)
Drought
An unusually long period without significant rainfall.
Some parts of the world, particularly between latitudes 10° and 35°, have a more variable rainfall pattern than others, and
so they can be said to be more drought-prone. These places include the Sahel region of Africa just south of the Sahara Desert, southern Africa, northeast Brazil, Australia, southern California, the southwestern United States, and India. Some places have seasons when rain never falls. They are called dry seasons, but they are not droughts. In these areas droughts occur in the rainy season when the rains do not fall as normal.
E
El Niño
A change in the tropical currents of the Pacific Ocean that prevents ocean water rising from the seabed and providing the nourishment
that ocean life needs (see: Ocean currents). This happens about once every five years, devastating ocean life and causing extensive climatic change.
 Drinking water—A sequence of settling and cleaning ponds and filter beds has to be used to make water fit to drink.
Erosion
The breakdown and removal of rock or soil—from a river bed, bank, or a sea cliff—by water.
Erosion may happen almost instantly, as in the case of a river scraping rock from its banks and carrying it away or a wave crashing against a cliff. It may also be a very slow process, such as when water causes rock to crack or break up (a process called weathering). In this case the disintegration of the rock is not followed immediately by movement. The broken material may simply form soil, and only many decades or centuries later is the soil carried away, perhaps by a river during a flood.
Direct river erosion of the river bed and banks is related to the energy of the water. Rivers reach their greatest energy during a flood, when there is a large amount of water moving at a high speed. At this time erosion can be severe and can lead to problems for people living close to a river.
There are many ways of trying to prevent erosion. One common
way is to reinforce the outside banks of meanders with concrete. (See also: Drainage.)
Estuary
A drowned river valley in a coastal lowland area.
Drowning occurs either because the land is sinking or from a worldwide rise in sea level, such as after the last Ice Age. An estuary
is a region of slack water where fresh water and seawater meet. It is very rich in wildlife. (See also: Water life.)
16
Evaporation
The change of water from liquid to vapor at temperatures below boiling.
Evaporation occurs because
the energy in warm air or sunlight can provide enough heat for water molecules to break free of the liquid that binds them together. As each molecule breaks free, it becomes part of the water vapor in the air. In this way liquid is changed into gas. This is the process behind the drying of a puddle or of clothes on a line.
Evaporation depends on the air being able to take up water