Every sovereign nation adopts its own set of standards, or “norms” for drinking water quality. The most influential and widely-recognized standards are those developed by the United Nations-World Health Organization, the European Union, Japan, and the United States EPA. They are all changed or updated regularly, so any listing here would be out of date quickly. There are always two types of regulations:
Primary requirements relate to health effects, and compliance is mandatory.
Secondary requirements relate to aesthetic effects and are only recommended.
In addition, the U.S. EPA also establishes maximum contaminant level (MCL) goals for some contaminants which for some reason cannot presently be attained. For example, all carcinogens are automatically given an MCLG of zero, even though everyone knows that zero is impossible to achieve.
In the United States, all water systems that regularly supply drinking water to at least 25 people or 15 “service connections” are Public Water Supplies which must comply with the regulations. If there is only one building or subscriber, such as a rural factory or school, it is a Non-Community Public Water Supply. If there is only one site and the 25 people are not necessarily the same 25 people every day, as at a rural restaurant or service station, it is a Non-Community, Transient Public Water Supply.