Because there is only limited amounts of fresh water on the Earth the rest is salt water; which humans can not survive on as the salt dehydrates our bodies instead of hydrates.
1) The more we try to get the the fresh water the more we will likely make more pollution.
2) The more we use the less there is.
3) Everything needs water.
Part 2; no idea I believe it is the ice caps, as it is fresh water in the ice caps and not a lot of humans up there to pollute the runoff.
