唔該,幫忙做關於water的PowerPoint,英文喎~~20分!!~~

How much water is there on, in, and above the Earth?
As you know, the Earth is a watery place. 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!

The vast majority of water on the Earth's surface, over 98 percent, is saline water in the oceans. But it is the freshwater resources, such as the water in streams, rivers, lakes, and ground water that provide people (and all life) with most of the water they need everyday to live. Water sitting on the surface of the Earth is easy to visualize, and your view of the water cycle might be that rainfall fills up the rivers and lakes. But, the unseen water below our feet is critically important to life, also. How would you account for the flow in rivers after weeks without rain? In fact, how would you account for the water flowing down this driveway on a day when it didn't rain? The answer is that there is more to our water supply than just surface water, there is also plenty of water beneath our feet.

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. Water from precipitation continually seeps into the ground to recharge the aquifers, while at the same time water from underground aquifers continually recharges rivers through seepage.

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 cropes, 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. Without ground water, people would be sand-surfing in Palm Springs, California. instead of playing golf.

http://www.hazelwood.k12.mo.us/~cdavis01/map2000/3rd/s16.ppt#256,1,投影片 1

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