the world i not only hungry， it i alo thirty。 thi may ound trange， ince nearly eventy percent of the earth' urface i covered with water。 but about ninety percent of thi i ea water。 man and mot of the animal can only drink and ue the remaining percent of water——freh water。the need for water i increaing day by day。 only tep are taken to deal with thi problem immediately can we avoid a evere world wide water hortage later on。 one of the firt tep i to develop way to reue it。
experiment have already keen carried out in thi field。 the ued witer ha been pumped to a water purifying plant。 there， it can be eparated from wate matter and treated with chemical o that it can be ued again， jut a if it were freh water from a pring。