The U.S. EPA has set standards for more than 80 contaminants that may occur in drinking water and pose a risk to human health. The contaminants fall into two groups according to the health effects that they cause.
Acute effects occur within hours or days of the time that a person consumes a contaminant. People can suffer acute health effects from almost any contaminant if they are exposed to extraordinarily high levels (as in the case of a spill). In drinking water, microbes, such as bacteria and viruses, are the contaminants with the greatest chance of reaching levels high enough to cause acute health effects.
Most people’s bodies can fight off these microbial contaminants the way they fight off germs, and these acute contaminants typically don’t have permanent effects. Nonetheless, when high enough levels occur, they can make people ill, and can be dangerous or deadly for a person whose immune system is already weakened.
Chronic effects occur after people consume a contaminant at levels over EPA’s safety standards over the course of many years. The drinking water contaminants that can have chronic effects include chemicals (such as disinfection byproducts, solvents and pesticides), radionuclides (such as radium), and minerals (such as arsenic). Examples of these chronic effects include cancer, liver or kidney problems, or reproductive difficulties.