Water is found all over the earth. In fact, about seven-tenths of the earth's surface is water! All living things need water. Your body is about two-thirds water.
             Ancient peoples thought water was an element, but it is not. Water is a compound of the elements hydrogen and oxygen. Both of these elements are gases at ordinary earth temperatures. In 1784, Henry Cavendish fund that hydrogen combined with oxygen to produce water. a few years later, scientists learned that a strong electric current would break water apart into hydrogen and oxygen. In a molecule of water, each atom of oxygen is attached to two atoms of hydrogen. Therefore the scientific formula for water is H O.
             Water has unusual properties. Other liquids become denser and heavier when they freeze. But water becomes less dense. That is why ice floats in water, instead of sinking. If ice sank, lakes and rivers would freeze from bottom to top. Nothing could live through the winter in a frozen lake or river. In seas near the North and South poles, great masses of ice would form on the bottom instead of floating on top. If this were to happen, there would probably be a permanent ice age on Earth.
             Water exists in three phases--as a liquid, as a solid (ice), and as a gas (water vapor). In temperatures at which most other natural substances are solids, water is a liquid. Its freezing point is 0 C (32 F), and its boiling point is 100 C (212 F). The boiling point is the temperature at which a substance changes into a gas.
             Nearly all other substances dissolve in liquid water this is very important to living things. Food and gases travel to and from a living thing's cells in water.
             Water is used in countless ways. Industry relies on water for all kinds of chemical processes. Water is used for cleaning, cooling, producing electric power, and for transportation and recreation.
             ...