People have wells at their homes, their water isn't being purified by someone else. Centralized supplies in the area are going to treat and monitor their water

People have wells at their homes, their water isn't being purified by someone else. Centralized supplies in the area are going to treat and monitor their water to ensure that it is below the applicable limits. It's reasonable to treat the aquifer home wells draw from as a public good and prevent contamination of it. Whether Amazon has particular responsibility in this case is a different question than that.