The Earth’s Waterworks

Did you know that every drop of water you drink or use has already been used many times? The same water has been recycled over and over again​—the process that sustains all living things on earth.

How Much Water Is There?

Water is so abundant that it is usually measured by the cubic mile. One cubic mile has more than 1,000,000,000,000 gallons, and there are 326 million cubic miles of water on earth.a

All but about 3 percent of this huge amount of water is in the mighty oceans. Of the 3 percent that is freshwater, over two thirds is locked up in the polar icecaps and glaciers. So the amount of water that is available and suitable for domestic, agricultural and industrial use is less than two thirds of one percent of all there is.

Of this small fraction, 97 percent exists underground, some as much as three miles down. Thus the water in all the streams, rivers, ponds, lakes and inland seas of the world adds up to less than one fiftieth of one percent of the total supply.

How Much Water Is Recycled?

Each year, the sun draws about 95,000 cubic miles of water from the earth​—80,000 cubic miles from the oceans and 15,000 cubic miles from land. This amounts to 3,600 million gallons a second. It returns to the earth as rain, snow, sleet, hail, frost and dew. Most of it falls right into the ocean, but about one quarter of it, or 24,000 cubic miles, comes down on land. From these figures, you can see that the land actually receives more water than it gives. The surplus is what keeps the rivers and streams flowing.

How Much Rain Does Fall?

If the rain that falls in one year came down all at once, the whole earth would be covered with three feet of water. The actual distribution, though, is very uneven. Annual rainfall varies from just 0.03 inches at Arica in northern Chile to 1,041 inches at Cherrapunji, India. However, it is the variation from year to year that creates the shortages that affect large numbers of people.

As a whole, the rain that falls on land in a year is more than 10 times the water in Lake Superior, the largest of the five Great Lakes in the U.S.A. It is enough to supply every person on earth with 17,000 gallons of freshwater each day​—a generous and abundant supply indeed. As in so many other things, the need is not for more, but for better management of what we have.

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