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Dehydration
The excessive loss of water from the body.
The human body is over 90% water. The body loses water all the time—about 1.2 liters a day—and it must be replaced. Normal water loss is replaced by drinking, and we do not give any thought to it. The body regulates the rate of replacement by making us feel thirsty. However, there are certain circumstances in which we do
not replace what we lose, and that results in a serious illness called dehydration.
Our bodies may lose excessive water by sweating, for example,
in a long race, or because we have gone through a long period without drinking such as in disasters when water supplies fail. Dehydration may be caused by an illness such as dysentery in which body fluids are rapidly lost.
Dehydration tends to cause a slow loss of body weight—about a kilogram a day. Once someone has lost about 13 liters of water,
The river spreads out over the delta.
sweating stops, and so the body loses its ability to get rid of
excess heat. As a result, the body temperature rises dramatically. Death from dehydration is therefore usually not by direct loss in body weight, but often by shock and heart failure due to a rise in body temperature.
The way to treat dehydration is not simply with water, but with a salt and water mixture. If it is given gradually, the body will then begin to recover.
Delta
A fan-shaped area of sediment built up at the mouth of a river. The world’s biggest deltas
include: Nile Delta, Egypt; Mississippi Delta; Ganges/ Brahmaputra Delta, Bangladesh; Mekong Delta, Vietnam; Yellow River Delta, China.
(See also: Drainage.)
 Delta—This side view of a delta
shows that it builds forward.
As the water enters the lake or sea, the sand spills over the delta and adds to the front of it.
The edge of the delta can be scoured by waves and water currents.
 Delta—Deltas can be categorized into fan or bird-foot shapes.
Desalinization
The removal of salt from seawater. Areas with few natural rivers,
such as deserts and islands,
use desalinization systems. Desalinisation is used in the Caribbean as well as in desert areas such as the Middle East.
Desalinization can be done by heating salt water until it boils. The vaporized water is then cooled, and the condensed water is collected. This is very costly in terms of energy and only suited to countries that have large reserves of cheap fuel.
An alternative process uses thin sheets of plastic, called membranes, that allow water to pass through them but keep the salt out. This process is not suited to seawater but works well with fresh water that has a high mineral content or when the water is slightly salty (“brackish”). This process is called reverse osmosis.
It is also possible to remove salt from water by freezing (see: Ice crystals). In areas where freezing temperatures do not naturally occur, this process also requires energy.
Mississippi Delta
Bird’s foot delta
Fan-shaped
Desalinization
Nile Delta
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