Drinking water can become contaminated at the original water source, during treatment, or during distribution to the home. This water is cleansed somewhat by exposure to sunlight, aeration, and micro-organisms in the water. Groundwater can be contaminated by disease-producing pathogens, leachate from landfills and septic systems, careless disposal of hazardous household products, agricultural chemicals, and leaking underground storage tanks. Examples of acute health effects are nausea, lung irritation, skin rash, vomiting, dizziness, and even death. Examples of chronic health effects include cancer, liver and kidney damage, disorders of the nervous system, damage to the immune system, and birth defects.
Evidence relating chronic health effects to specific drinking water contaminants is limited.
In the absence of exact scientific information, scientists predict the likely adverse effects of chemicals in drinking water using human data from clinical reports and epidemiological studies, and laboratory animal studies. Its main provisions directed the EPA to establish minimum drinking water standards to limit the amounts of various contaminants found in drinking water. Because of growing concerns about the safety of the water supply, amendments were made to strengthen this law in 1986. MCLGs are nonenforceable health-based goals and represent the maximum level of a contaminant that is expected not to cause any adverse health effects over a lifetime. MCLs are enforceable contaminant levels.