Water is very important to us. Factoriesand plants need water for industrial uses, and large pieces of farmland need itfor irrigation. Without water to drink, people die in a short time. Today mostwater sources are so dirty that people must purify water before drinking. Waterbecomes dirty in many ways: industrial pollution isone of them.

With the development of industry, plantsand factories pour tons of industrial wastes into rivers very day. The rivershave become seriously polluted, and the water is becoming unfit for drinking orirrigation. The same thing has also happened to our seas and oceans. So theproblem of water pollution is almost worldwide. Scientists of many countrieshave done a lot of work to stop pollution. The polluted water in some placeshas become clean and drinkable again. Perhaps one day, the people in all townsand cities will be drinking clean water. That day, we believe, is not very faroff.