1.  We don't be used of looking this.

2.  In our every day life, for example, if we first use knife for the first time, we can't use it well, if we try to use it for several times .

3.  Fresh water can never be used up.

4.  In people's eyes, fresh water can not be used up.

5.  Thus, the polluted water can not be used.

6.  We dare not use these water, because it is harmful to our health.

7.  Certainly, Fresh water will never be used up.

8.  The polluted water can't be used by people.

9.  Some can not be used.

10.  This poison water can't be used.