The above responses seem to indicate that I wasn't too clear about my question...
Revised question: Due to what appears to be a porous interior, if you pour cow-poop-contaminated river water into the tank, is the tank contaminated forever after, no longer usable as a source of drinking water?
Sue
Nice reframe! LOL! I'd be very hesitant. Makes me wonder, if the answer is "Yes, it can be usable again", How? Once you've contaminated a container like that, how can you un-contaminate it?
Maybe the trick it to take all the potable water out of the tank before you flush with non-potable?