How Effective is the TCR in Assessing Outbreak Vulnerability?

Previous studies have shown that waterborne disease outbreaks can occur in systems that have not exceeded the maximum contaminant level (MCL) regulations for coliform bacteria. The utility of the revised Total Coliform Rule (TCR), which has been in effect since Dec. 31, 1990, was evaluated as an indicator of outbreak vulnerability of public water systems. This study compared TCR violations for water systems that had and had not reported an outbreak during 1991-98. Few outbreak systems had violated the MCL in the 12-month period before the outbreak, and MCL and monitoring violations did not differ significantly for the outbreak and nonoutbreak systems studied. These findings suggest that the TCR is not able to identify those water systems that are vulnerable to an outbreak. Requirements may need to be supplemented by an additional indicator and additional monitoring for systems that currently collect few samples. When evaluating the adequacy of an indicator, it is important to consider waterborne agents and the frequency of sample collection. The thoroughness of a sanitary survey is also important to detect and correct deficiencies that might lead to an outbreak. Current TCR monitoring focuses on the detection of coliforms in the distribution system after treatment; however, it may be more effective-especially for small groundwater systems-to monitor source water quality and assess the potential for contamination from sewage discharges and surface water runoff rather than to increase distribution system monitoring.