412

9.
10. solution
13. a.2.11% b.0.009%
14. ocean, glaciers, water vapor, rivers
15. yes
16. Well, it is possible because water molecules do not just disappear.

495

1. Purifying water is taking out all of the bad bacteria and diseases.
2.boiling, adding chlorine, and filtration
3. bacteria and minerals
4. a. Too much salt b.boiling
5.
6. Yes it has, because we keep using it more and more.
7.ocean water
8. Land will dry out because the water will flow to the ocean.

11.
12. in order to prevent horrible effects
13. fluoride is added to reduce tooth decay
18. Untreated water is very bad because it can be harmful to the human body.
19. It will cause trihalomethane's.