I now live in the Netherlands, but I'm from Poland and had no idea about that.<br>I was born and lived in Krakow, which took it's water from various springs, underground wells and reservoirs. Due to that water was of very good quality (however it had some limestone in it, AKA hard water).<br>Most of our sewage was filtered then put into Vistula river, that was then going to Warsaw and their water treatment plant was supplying the whole city with water from Vistula. I guess they had it more challenging, as the river contained a lot of contaminated water.