This thread is on the right track ... but the challenge is a bit bigger than people are thinking.

Let's suppose you are really thirsty in an urban environment, and you have no access to bottled water or any "normal" form of clean water. Therefore - you need to scavenge water from some other source. Then you have to purify it.

If you get the water from a place like a pond at a local park, then probably a water purifier might work fine. Same thing goes for water from hot water heaters.

But if you only have pools of water sitting stagnant in the city, then you've got the possibility of real contamination. Pollution ... chemical contamination. I'm not sure that a still will really separate all possible contaminants.

Pete