Safety of tap water varies considerably by location; some people have to be concerned about consuming tap water.
I look at fish as canaries in a mine. I can kill off a number of small fish and cause my large fish great discomfort just by NOT pre-mixing my water conditioner before a water change.
My water company in Philadelphia primarily draws water from the Schuylkill river. The Schuylkill has > 80 waste treatment plants along the 110 mile river length. It has farm, lawn, and industrial run off. It is also mixed with abandoned coal mile water (acidic and heavy mineral content) about six months out of the year to supplement the water flow for use by a nuclear reactor.
The river is essentially dead by the time it reaches Philly. My daughter is on a crew team for a Philly University and for years I have yet to see a single fish (not even a minnow) in the river; even looking under the 50' launch pier.
I watched that City Limits Fishing show on TV when they came to Philly. They fish for 5 hours in rivers within city limits. After 4 hours in Philly, he didn't even have a single bite. Then he landed a good size bass and declared fishing is great in Philly. What he did was to find a large pipe that was draining natural spring water into the river. He caught the bass inside the pipe.
BTW - I drink Deer Park spring water.
For those who say water is safe coming out of a waste treatment plant; I attached Google Earth pictures of two waste treatment plants up stream. That white foamy water can't be safe to drink.
