In the United States, public drinking water is regulated by the U.S. Environmental Protection Agency (EPA). Additional regulation is also enforced by individual states. The EPA is responsible for studying potential contaminants, also referred to as constituents, and determining whether they may be harmful to humans. According to the Safe Drinking Water Act, a contaminant can be any physical, chemical, biological or radiological substance or matter in water; it can be organic or inorganic. The Act requires that the EPA follow a specific process in order to identify unregulated contaminants.

Every five years, the EPA determines what necessary and potentially harmful constituents may be found in drinking water and are added to the Contaminant Candidate List (CCL). The CCL is later narrowed down to approximately 25 to 30 contaminants. All items on the list are then required to be tested by public water agencies and certified laboratories, based on schedules instructed by the EPA.

“As mandated by the EPA, public water districts are responsible for the monitoring and testing of constituents of emerging concern based on current and relevant potential contaminants,” shares Amy Mora, Senior Environmental Analyst at Eastern Municipal Water District. “This is important to note because the contaminants being studied are not from an outdated list, they are based on what may be found in existing water systems based on environmental and external factors.”

The process of sampling is specified by the Unregulated Contaminant Monitoring Rule (UCMR). Following the submission of the results to the EPA by water agencies, the EPA decides on a regulatory determination to establish if each contaminant listed requires regulation based on the amount that is detected in drinking water. The scientific data collected is one of the primary sources for determining regulations concerning emerging constituents.

“Research on constituents is an on-going process,” continues Mora. “As trained scientists, we are educated to study the contents in our drinking water. Water agencies also rely heavily on testing analysis from certified laboratories.”

According to the EPA, currently there are approximately 6,000 public water systems in the U.S. participating in the UCMR sampling process. Monitoring of potentially harmful contaminants is a critical step in ensuring the safety of public drinking water by states, tribes and water systems. While small amounts of contaminants are usually traceable in public water systems, not all are harmful. Further testing is needed prior to verifying potential health risks and what amounts are determined to be harmful. The overall compilation of the contaminant list, followed by monitoring and water testing are the initial steps to reviewing relevant constituents that could be potentially harmful to humans.

If a public water system monitoring program finds contaminants during testing, information is included in the water agency’s consumer confidence report. The consumer confidence report will list all regulated, as well as unregulated contaminants. The EPA requires public water agencies to provide consumers with an annual confidence report. This report provides information concerning the water quality of the drinking water supply over the previous in year. In California, agencies are required to post and/or mail reports to customers by July 1. Californians can check the website of their local water agency for specific information pertaining to their home or business.