11.  And the politicians should take measures to prevent fresh water from being polluted, being wasted.

12.  Second, we should prevent fresh water from pollution.

13.  Thirdly, we'd better do our best to prevent fresh water from being polluted further.

14.  Second, we should take steps to prevent fresh water from poluting again.

15.  In addition, we must prevent water from being polluted.

16.  Second, we must protect our surroundings and prevent fresh water from pollution.