Estimates vary, but somewhere between 70 and 75 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 (view a graphic of 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! When you take a look at the water around you, you see water in streams, rivers, and lakes. You see water sitting on the surface of the earth. Naturally, this water is known as "surface water." Your view of the water cycle might be that rainfall fills up the rivers and lakes. But, 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 water stored in the ground than there is 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 85 billion gallons per day of ground water. In a way, that underestimates the importance of ground water, since not only does ground water help keep our 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, Ca. instead of playing golf! Just how much water is there on (and in) the Earth? Here are some numbers you can think about: The total water supply of the world is 326 million cubic miles (a cubic mile is an imaginary cube (a square box) measuring one mile on each side). A cubic mile of water equals more than one trillion gallons. About 3,100 cubic miles of water, mostly in the form of water vapor, is in the atmosphere at any one time. If it all fell as precipitation at once, the Earth would be covered with only about 1 inch of water. The 48 contiguous United States receives a total volume of about 4 cubic miles of precipitation each day. Each day, 280 cubic miles of water evaporate or transpire into the atmosphere. If all of the world's water was poured on the United States, it would cover the land to a depth of 90 miles. Of the freshwater on Earth, much more is stored in the ground than is available in lakes and rivers. More than 2,000,000 cubic miles of fresh water is stored in the Earth, most within one-half mile of the surface. Contrast that with the 60,000 cubic miles of water stored as fresh water in lakes, inland seas, and rivers. But, if you really want to find fresh water, the most is stored in the 7,000,000 cubic miles of water found in glaciers and icecaps, mainly in the polar regions and in Greenland. Where is Earth's water located? see link for info http://ga.water.usgs.gov/edu/earthhowmuch.html