A ground water system will be subject to triggered source-water monitoring if its treatment methods don't already remove 99.99 percent of viruses. Systems must begin to comply with the new requirements by Dec. 1, 2009.

The rule outlines risk-targeting strategies, including regular sanitary surveys of public water systems, triggered source-water monitoring, and monitoring systems to ensure effective pathogen removal.

Contaminants in question are pathogenic viruses and bacteria. Utilities will be required to look for and correct deficiencies in their operations to prevent contamination from these pathogens.

For more information on the new ground water rule, visit epa.gov/safewater/disinfection/gwr.