[إيليا]

Water

Water is the most important liquid in the world. Without water, there would be no life, at least not the way we know it. This source of life makes up about three quarters of the human body. Water contains various minerals - some good for your health, others less so. Explore the different ingredients of bottled waters. Some 70% of the earth is covered with water. But nearly all is unavailable for human consumption without being processed first. The oceans make up for 97% and the polar ice shields hold another 2%. Only about 1% is soft water from lakes rives and underground sources, but even from that tiny amount an increasing part is unsafe for human consumption. Water is of major importance to all living things; in some organisms, up to 90 percent of their body weight comes from water. Up to 60 percent of the human body is water, the brain is composed of 70 percent water, and the lungs are nearly 90 percent water. About 83 percent of our blood is water, which helps digest our food, transport waste, and control body temperature. Each day humans must replace 2.4 liters of water, some through drinking and the rest taken by the body from the foods eaten. The unique qualities and properties of water are what make it so important and basic to life. The cells in our bodies are full of water. The excellent ability of water to dissolve so many substances allows our cells to use valuable nutrients, minerals, and chemicals in biological processes.
About 70 percent of the Earth's surface is water-covered. But water also exists in the air as water vapor and in the ground as soil moisture and in aquifers. Thanks to the water cycle our planet's water supply is constantly moving from one place to another and from one form to another. Things would get pretty stale without the water cycle! Even though you may only notice water on the Earth's surface, there is much more freshwater stored in the ground than there is in liquid form on the surface. In fact, some of the water you see flowing in rivers comes from seepage of ground water into river beds. Humans are happy this happens because people make use of both kinds of water. In the United States in 2000, we used about 323 billion gallons per day of surface water and about 84.5 billion gallons per day of ground water. Although surface water is used more to supply drinking water and to irrigate crops, ground water is vital in that it not only helps to keep rivers and lakes full, it also provides water for people in places where visible water is scarce, such as in the desert towns of the western United States.
Earth's water is always in movement, and the water cycle, also known as the hydrologic cycle, describes the continuous movement of water on, above, and below the surface of the Earth. Since the water cycle is truly a "cycle," there is no beginning or end. Water can change states among liquid, vapor, and ice at various places in the water cycle, with these processes happening in the blink of an eye and over millions of years. Although the balance of water on Earth remains fairly constant over time, individual water molecules can come and go in a hurry. The water in the apple you ate yesterday may have fallen as rain half-way around the world last year or could have been used 100 million years ago by Dinosaur.


Total water use in the United States for 2000 was determined from estimates of water withdrawals for the eight categories of public supply, domestic, irrigation, livestock, and aquaculture, industrial, mining, and thermoelectric power. Total freshwater and saline-water withdrawals for 2000 were estimated to be 408,000 million gallons per day (Mgal/d), or 457,000 thousand acre-feet per year. Freshwater withdrawals were 85 percent of the total, and the remaining 15 percent was saline water. Estimates of withdrawals by source indicate that for 2000, total surface-water withdrawals were 323,000 Mgal/d, or 79 percent of the total withdrawals for all categories of use. About 81 percent of surface water withdrawn was freshwater. Total ground-water withdrawals were 84,600 Mgal/d, of which 99 percent was freshwater. Nearly all (98 percent) saline-water withdrawals were from surface water.

The top row of cylinders represents where America's water came from (source) in 2000, either from surface water or from ground water. You can see most of the water we use (262,000 million gallons per day (Mgal/d)) came from surface-water sources, such as rivers and lakes. We used about 83,400 Mgal/d of ground water (from wells). The pipes leading out of the blue and brown cylinders on the top row show where the water was sent after being withdrawn from a river, well, etc. For example, the blue pipe coming out of the surface-water cylinder and entering the Public supply grey cylinder shows that 27,300 Mgal/d of water was withdrawn from surface-water sources for public-supply uses. Likewise, the brown pipe shows that public-suppliers withdrew another 16,100 Mgal/d of water from ground-water sources. Each green cylinder represents a category of water use. The Industrial cylinder, for instance, shows how much water the United States used, each day, by industries. In 2000, about 18,500 Mgal/d of water was used for industrial purposes, with about 14,900 Mgal/d coming from surface water and about 3,570 Mgal/d coming from ground water. So, now you maybe see how the two "Source" cylinders on the top row show how much water was withdrawn from the environment, and, for each water-use category (the green cylinders), the water arrives via the pipes