Pharmaceuticals, personal care products, and other manufactured compounds are constituents for which regulatory standards have not been developed, could potentially affect people and/or aquatic life, and have been detected at low concentrations in surface and groundwaters.

Establishing where emerging contaminants might pose risks and how those risks might compare to better known issues is important for prioritizing follow-up studies and management activities. Studies conducted by GAMA (Fram and Belitz, 2011), found pharmaceutical compounds in much smaller portions of the state's groundwater resource (3.3% of 855 samples of modern groundwater) than pesticides or volatile organic compounds, and most often in densely urbanized areas. Extensive water recycling in Los Angeles area groundwater basins may explain why pharmaceuticals are detected at a higher frequency there than in other urban areas.