1.  Most people usually tend to think that fresh water can never be used up, especially when they consider the fact that we can obtain fresh water from such resources as rainfall , river flowing and well water .

2.  However in fact , fresh water is in a critic shortage, nowadays.

3.  With the dramatically increasing of population and the amount of industry using water, more fresh water is used everyday.

4.  Hence something must be done to avoid the future disasters that the shortage of fresh water would bring to us.

5.  Nowadays people usually think that fresh water in the earth will be plentiful for ever.

6.  Many people argue that there are so many rivers and wells in the world that human beings May have a plenty of fresh water to use.

7.  So it makes up for the used fresh water.

8.  But in fact, the problem of fresh water shortage is becoming more and more serious today.

9.  Firstly, overpopullation has caused the fact that there are more and more people who will need much fresh water year by year.

10.  Secondly, the need of fresh water in industry is increasing.