#1-9, 18-22

1. See paper

2.
Evaporation: removes nearly all dissolved substances (dissolved heavy metals, minerals, or molecular substances)
Precipitation: pure water vapor condenses and falls as either rain or snow, which is the purest water on Earth.
Sand and gravel filtration: pure rainwater goes through sand and gravel when it reaches the ground and the sand and gravel serves as a filter, removing nearly all suspended matter in the water.

3. Aluminum hydroxide causes the water to clump together and sink to the bottom. It forms a sticky, jellylike substance that traps and later removes the suspended particles. They obtain the water that is now free of suspended particles by sand filtration.

4. CaO is sometimes added in the final steps of municipal water treatment to neutralize acidic water, which raises its pH to the acceptable level for drinking.

5. There is a limit of 1 ppm of fluoride that can be added to water. The purpose of the fluoride is to reduce tooth decay.

6. The bacterial in chlorinated drinking water has been killed compared to untreated water which may very likely still contain diseases and microorganisms. The bad taste of the chlorinated water is worth the safety that it brings us.

7. The disadvantage is that THMs can develop in over-chlorinated water and this is known to cause cancer in very high concentrations.

8. Even though the water that comes down the stream is initially pure as rain or snow, once it hits the ground it is immediately contaminated. The water could carry diseases from the ground, bacteria, or from plants and animals.

9.
Charcoal filter: charcoal filtration can remove most organic compounds from water (including THM)
Ozone or an ultraviolet light: can completely eliminate chlorine, however it is not effective once the water leaves the ultraviolet light.

18. It would be very hard to get pure water because evaporation is a very effective way of naturally filtering water of all impurities. Clean water would become much rarer and more expensive because more technology would have to be used in order to make pure water.

19.If water could not turn into a gas, it would not be able to evaporate. If water could not be a liquid, there would be nothing to drink and there would not be any rain or snow. There would not be pure water. Mostly, humans would not be able to live if there was not water because it is an essential liquid that we need to survive.

20. It does not completely prohibit the use of chlorine because chlorine can be very benefitting towards us because it protects us from catching water-bourn diseases. If the amount of THM is relatively small, it is not very harmful to us.

21.
Evaporation is very similar to water distillation. Water is being turned into vapor as a purifying method in both processes. Sand and gravel filtration is similar to the sand filtration we did in the lab, along with charcoal filtration which we performed in our experiment and is also naturally occurring on Earth.


22.
a. one day: 1 ppm
b. one week: 7 ppm
c. one year: 365 ppm