The tap water in Piter is supposed to be potable, but nobody drinks it. My eldest son was going to school in Kolpino for some months, the parents was sharing the costs for a water dispenser in the class room. I don't remember what they used for drinking it. We've also installed a filter for drinking water. Actually I think it makes sense to do the filtering locally and only for the drinking water, in Norway quite some money is spent on making sure the water is potable, even if only a small percentage of the water is actually drunk - and even here we can't trust the water supply, there was a big scandal in one municipality this summer, some people probably died due to the bad water quality.