Comment by saaaaaam

Water companies used to be publicly owned until Thatcher privatised them. Unfortunately, as they are a natural monopoly (you cannot choose which company to supply your water services apart from moving to a different part of the country), the companies have basically been extracting as much money as possible from the public and not investing in the infrastructure. This has led to ridiculous bills for water and disastrous performance in terms of not pouring sewage into waterways. The classic example is Thames Water which is now saddled with incredible debts and is asking for yet more money to invest in infrastructure (which they didn't do all the other times they asked for more money).

Generally water nationalisation means nationalising the companies which supply water to homes and businesses. Not, er, literally nationalising water as in the substance.