Look! People are gathering to get water from a huge well in the village of Natwarghad in the western Indian state of Gujarat! ①Because of the large population on the earth, the world is ________hungry, it is ______be thirsty for water now. The world's population has reached 7 billion. And it could possible grow to 15 billion by the year 2100.

   ②On the other hand, about 97% of water on the earth is sea water which we can't drink or use for watering plants directly.Man can only drink or use the other 3% of fresh water which comes from rivers, lakes and underground. And we can't even use all of that, because some of them has been polluted.

    Now more water is needed. The problem is: can we avoid a serious water shortage later on? Firstly, we should all learn how to save water. Secondly, we should find out the ways to reuse it. Today, in most large cities water is used only once, but it can be used again .Even if every large city reuse its water, still there would not be enough. What could people turn to next?

    The sea seems to have the best answer. The sea is very big. Look at the map of the world, there is more sea than land. It covers three quarters of the earth. All that needs to be done is to get the salt out of the sea water. Scientists are trying to find a cheaper way of doing it. So you see,③如果我们可以找出解决方法，我们就不会有干涸（dry up）的危险。