WHO has published a fascinating review of regulations and standards for drinking water quality
in 104 countries and territories, representing c 89% of the world's population, and their comparison with WHO Guidelines on Drinking Water Quality or WHO Health-based Values. The review shows a wide range of values and parameters being regulated for the different countries and frequent instances of values set higher than WHO guidance. For microbiological parameters only 1 country has not set a value for E.coli
while at the other extreme only single countries have set limits for one or more of amoeba, Vibrio cholera
, free living organisms, helminths, Legionella
, nematodes, parasites and plankton. Several countries have set values for parameters such as total heterotrophic bacteria, hardness or potassium for which WHO has considered it is not appropriate to set a value, while lead is one of only three parameters for which all 104 countries have set a value.