Joe, there used to be a Army surplus place out Winchester road that sold food grade barrels, I think I paid 15 or 20 bucks for mine. I used them for everything from holding water to raising fry. Just bleach them a few times, rinse and let them dry out and they should be ready to go. You might try the Coke distributor as well, that was where mine came from and the place on Winchester Road bought them in bulk. I always ran a Mag 350 full of charcoal instead of a powerhead, couldn't hurt.
I haven't had any trouble with the water, usually it's an overdose of chloramines that they put in, a double dose of Prime and a few minutes with an airstone usually fixes it. Our water company is bad about just putting all kinds of crap in the water and not bothering to tell anybody. How big are the water changes you were doing? I never run straight cold tap, I just adjust the temp to 75 or so and don't have any trouble, even in my shrimp tanks. I do 10-20 percent water changes on 8 tanks every week and havent' had any problems with losing fish.
Oh, and the reason it says "do not drink" is probably the same reason my wife's hair straightener says, "Caution, may burn eyes." (that hair straightener cracks me up, it also says "In Canada-DO NOT USE INDOORS")Because people do some dumb things and if it didn't say do not drink there would invariably be some cases of people drinking stagnant rain water from the thing, getting sick and then sueing the company that makes it... If it's made from ABS plastic it's more than likely fine, if you want to test it just fill it up, dechlor it and put a few goldfish in.