The water on the earth is recycled constantly in a process known as the hydrologic cycle. First, the water in the oceans evaporates. It changes into vapour and forms clouds in the sky. Water accumulates in clouds and returns to the surface of the earth in some form of  precipitation, which can be either rain, snow, or ice.

When the water reaches the earth’s surface, it runs off into streams, rivers, lakes, and at last, into the oceans, where the cycle begins again. The water on the surface of the eartli and in the atmosphere is known as the hydrosphere. Not all precipitation goes into rivers.

Some of it seeps  into the ground by a process called infiltration. This water collects under the earth’s surface and is groundwater. Groundwater is important for two reasons.

First, 95 per cent of the earth’s water is in the oceans. It is salty and useless for plants, animals, or humans. Fresh water, which people can use for drinking or for  agriculture, is either on the earth’s surface in lakes and rivers or underground. Surface water is .05 per cent of the earth’s water while underground water is 4 per cent of the earth’s water.

Consequently, groundwater provides 95 per cent of the available fresh water on the earth.

Second, groundwater is important not only because of the size  of the supply, but also because of its dependability. It is always available since it does not depend on seasonal precipitation. Today, there seems to be a problem with groundwater. Until recently, groundwater was clean. It was not necessary to purify it before people drank it.


However, for many years, people have been  burying garbage and poisonous wastes underground. These poisons have polluted the groundwater in many places. Therefore, it is unsafe for human use unless the dirty and harmful substances are removed first. Aquifers are geologic formations that allow groundwater to  accumulate and move through them.

Although they are often called underground rivers, these formations are not like surface rivers. The water accumulates in one area underground. The amount of water an aquifer contains is enough to be easily pumped out for use.


People have been using groundwater for many years. With an  increasing population, the need for water has also increased. Some cities depend only on groundwater for their water supply. They are using underground water very quickly. In some places the water supply may soon be used up, and there will be no water for a large population. One example of this is Tucson, Arizona, which is located in the Sonora desert in southwestern United States.

It is on a very large aquifer which supplies water for the area at the present. The aquifer provides water for an increasing population in the city and for agriculture throughout southern Arizona. At the present time, the city is using 225,000 acre feet of water per year, 75,000 acre feet are being  returned to the aquifer through the natural processes of the hydrologic cycle.

Therefore, people are using about three times more water than nature is supplying. The water table, which is the level of the water in the aquifer, is dropping lower every year. Some wells have already gone dry and have either been closed or drilled deeper.

Scientists  predict that the supply of water in the aquifer will run out in twenty to eighty years. Aquifers contain a generous supply of water. They are large, easily available, and mostly clean. Still, people who depend only on aquifers for their water supply must use their water carefully. Their lives and  their children’s lives depend on conserving the water they have.


A. What do the following mean?

1. ‘infiltration’ (line 10): the process by which

2. ‘groundwater’ (line 11):

3. to purify (line 23): to

4. to provide (line 42): to

5. ‘conserving’ (line 60):


B. Mark the statements as True (T) or False (F).

1. Precipitation can be in various forms.

2. Groundwater exists whether there is precipitation or not.

3. Oceans contain 95 per cent of the fresh water on the earth.

4. As groundwater is polluted, people do not use it any more.

5. Groundwater moves through aquifers.

6. In surface rivers the water accumulates in one area.

7. Half of the water that people in Tucson use returns to the aquifer.

8. Tucson is an agricultural area.

9. ‘Water table’ is a term related to the level of water in a well.



1. Write two sources of fresh water that are on the earth’s surface.
2. How do people obtain water from an aquifer?
3. What happens to a well that goes dry?

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