MCLGs allow for a margin of safety. The concentration of a contaminant which, if exceeded, triggers treatment or other requirements which a water system must follow. It is found all over the U.S.A. It can move from the ground into a home through cracks and holes in foundations. The disinfection process is carefully controlled and monitored so that it remains effective, while keeping the levels of disinfection by-products low. To ensure that tap water is safe to drink, EPA prescribes limits on the amount of certain contaminants in water provided by public water systems.
Federal regulations establish limits for contaminants in bottled water.
Drinking water, including bottled water, may reasonably be expected to contain at least small amounts of some contaminants. The presence of contaminants does not necessarily indicate that water poses a health risk. As water travels over the surface of the land or through the ground, it dissolves naturally-occurring minerals and radioactive material, and can pick up substances resulting from the presence of animals or from human activity. Inorganic contaminants , such as salts and metals, which can be naturally occurring or result from urban storm runoff, industrial or domestic wastewater discharges, oil and gas production, mining or farming. Pesticides or herbicides , which may come from a variety of sources such as agriculture, storm water runoff, and residential uses.