The world is nor only hungry，but it is also t 1  for water．This may seem strange to you，since nearly 70％of the earth is c 2 with water：But about 97％of this huge amount is sea water，or salt water．Man can only drink and use the other 3％——the fresh water from rivers，lakes，

underground，and other sources. Even w 3 ，some of it has been p 4 ．Now our need for water is i 5  -almost day by day．We must take steps to solve this prob1em，or we can’t a 6 a worldwide water shortage later on．

We all have to learn how to  s 7  water．One of the first steps is to develop ways of reusing it．

Today in most large cities，water is used only o 8  and then sent out into a sewer system(下水道)．But it is possible to get used water to a purifying(净化)factory．There it can be purified so t9   it can be used again．

    The world’s water shortage is a big p10 for humans．We must save every drop of water and keep our rivers and lakes clean．