Water, the most common substance on Earth's surface. It also covers more than 70 percent of Earth's surface area and exists as vapor in Earth's atmosphere. It is essential to life and greatly influences weather and climate. Water plays an essential role in many chemical reactions.

Water is used to provide hydroelectric and steam power. In rivers, lakes, and oceans it forms important avenues of transportation. As rain and ice, it wears down hills and mountains, and helps convert rocks into soil. We drink water, and use it in cooking, washing, heating, fighting fires, treating diseases, and many other ways.

The first living things appeared in water. For a very long time there was no life on earth except in water; life is still more abundant in water than on land. All living things are composed chiefly of water. An adult man, for example, consists of 65 to 75 per cent water. Water carries food to body cells and carries wastes away from them. It also helps the body maintain an even temperature. The loss of more than 15 to 20 per cent of the body's water usually results in death.

Water has symbolic meanings in many religions. In Christian baptism, water is used to symbolize the washing away of sin. To Jews, water is a symbol of purity; to Hindus, a symbol of fertility. Taoists regard water as the symbol of humility, because it always seeks the lowest place.

Interesting facts about water
How much water is on the earth? There are about 326 million cubic miles (1.4 billion cubic kilometers) of water. There are over a million million (1,000,000,000,000) gallons of water per cubic mile (0.9 million million liters per cubic kilometer).
How much of the earth's water is fresh? Only about 3 percent of the earth's water is fresh. About three-fourths of the earth's fresh water is frozen in icecaps and other glaciers. Glaciers contain as much water as flows in all the earth's rivers in about 1,000 years.
How much water do living things contain? All living things consist mostly of water. For example, the body of a human being is usually 50 to 75 percent water. An elephant is about 70 percent water. A potato is about 80 percent water. A tomato is about 95 percent water.
How much water does a person take in over a lifetime? On the average, a person takes in about 16,000 gallons (60,600 liters) of water during his or her life.
What are the different forms of water? Water is the only substance on earth that is naturally present in three different forms--as a liquid, a solid (ice), and a gas (water vapor).
How much water does a person use every day? On the average, each person in the United States uses more than 100 gallons (380 liters) of water a day in the home.
What is the largest single use of water? The largest single use of water is by industry. It takes about 80 gallons (300 liters) of water to make the paper for one Sunday newspaper, and about 20 gallons of water per pound (170 liters per kilogram) of steel produced.
Can water ever be used up? Water is used and reused over and over again--it is never used up. Every glass of water you drink contains molecules of water that have been used countless times before.