The world is not only hungry, hut also thirsty for water. This may seem strange to you. since nearly 75 % of the earth's surface is covered with water. But about 97% of this huge amount is sea water, or salt water. Man can only drink -and use the other the fresh water that comes from rivers, lakes.underground- and other sources. And we cannot even use all of that, because some of it is in ihe form of icebergs and glaciers. Even worse, some of it has been polluted.

　　However, as. things stand today, this small amount of fresh water, which is constantly being replaced by rainfall, is still enough for us. Hut our need for water is increasing rapidly almost day by day. Only if wc take steps to deal with this problem now can wc avoid a severe worldwide water shortage later on. A limited water supply would have a bad effect on agriculture and industry. Let rne give you just one small example of how necessary water is to industry. Did you know that to produce a single ton of steel, il takes about 91*000 liters of water?

　　We all have to learn how to stop wasting our precious water. One of Ihe first steps wc should take is to develop ways of reusing it. Experiments have already been done in this field, but only on a small scale. For us. the systems are as important as the spacecraft.