Knowledge is power
There are a number of sites for finding out how your community stacks up on a variety of environmental factors. Today I discovered Scorecard, which gives in-depth reports on toxics, water quality, air quality, and environmental justice in any zip code you choose. It also provides a sliding scale showing where your community falls relative to other communities in the nation. Mine is pretty bad by most measures, which is depressing.
Another good site is SustainLane Government, which provides a yearly scorecard for major cities based on factors such as public transportation, green building, and planning. Again, my city ranks near the bottom.
Finally, if your interest is in water quality specifically, EPA's Surf Your Watershed provides a wealth of information, not only on the status of water quality but also about organizations you can get involved with to help monitor water quality and to help with cleanups and advocacy.

Comments
in a global sense i think about the lack of access to potable water for the majority of the world. for example, more children die every year due to lack of access to clean water than anything. its really sad. and we use drinkable water to flush our toilets and wash our cars in america!
in a local sense i also think about the quality of the water going thru the pipes in my building. my apartment building is old and the water coming out of the pipes is nastier than anywhere else ive seen, drank, smelled or touched water in the city. we installed a water faucet filter on our kitchen sink for now. its at least one thing you can do to improve the quality of water in your home.