The drinking water regulations require that all public water supply systems test for a variety of contaminants in drinking water. For many of the contaminants, the U.S. Environmental Protection Agency (EPA) has set enforceable standards for the maximum amount allowed in drinking water. These standards are based on possible health effects of consuming the water. The standards are known as maximum contaminant levels (MCLs), and are published as national primary drinking water regulations (NPDWR).

The MCLs are set at levels at which no significant health effects would occur if water was consumed for an entire lifetime. The MCLs are set by EPA, and then adopted by the State. The State must adopt MCL standards at least as stringent as EPA, but may adopt more stringent standards.

Although standards have been set for many contaminants, some contaminants which may occur in drinking water have not yet had NPDWR MCLs standards established. The EPA still requires systems to test for some of these "unregulated" contaminants, and report on their testing.

Even though MCLs have not been set for the "unregulated" compounds, many of them have been studied by EPA for both their acute health effects and in some cases for their long-term effects, which may involve carcinogenic or noncarcinogenic effects.

All water served by the Board of Water Supply (BWS) is tested by the DOH in accordance with NPDWR. In addition to that, we also conduct routine examinations of our waters for salt water intrusion. This program manages our natural drinking water resources by protecting them from overpumpage. The DOH's enforcement of the NPDWR testing enables both the DOH and BWS to cover a wide range of drinking water issues. DOH focuses on NPDWR testing, while the BWS performs all salt water intrusion monitoring, treatment plant operations, and distribution system testing.