Natural protection of spring and well drinking water against surface microbial contamination. II. Indicators and monitoring parameters for parasites.

Recent outbreaks of cryptosporidiosis and reports of other newly described para-sitic diseases associated with drinking water transmission prompted a reevaluation of source water monitoring criteria for public health protection. The field of microbial indicators was reviewed and each candidate sentinel evaluated in terms of its sensitivity, specificity, and technical feasibility. In addition, a clear distinction was made between source water monitoring and monitoring in the distribution system. Of all potential candidate microbial sentinels, Escherichia coli is deemed the most efficacious for public health protection. Based on a conservative estimate of its half-life in groundwater for 8 d, it is recommended that at least two samples be obtained during this half-life. In addition to E. coli, two water quality indicator sentinels, which are not necessarily direct public health threats, should also be monitored at the same frequency. These are the total coliform group and the enterococci. If E. coli is present in any source water sample, the borehole and any directly connected borehole should be embargoed. If either total coliforms or enterococci are detected, only that individual borehole should be taken off line and not used until the situation is remediated and the cause of the fecal contamination eliminated. Clostridium perfringens spores serve as a useful long-lived indicator. However, their perseverance in a sample should not be considered a direct public health threat because spores may far outlive pathogens. As a parasite indicator, C. perfringens should have the same importance as a positive coliform or enterococcus analysis. Coliphages do not yet fulfill enough of the criteria to be routinely employed. Biological monitoring should be coupled with physicochemical monitoring to establish a long-term history of the source. Because all natural waters vary in the amounts of heterotrophic plate count bacteria, test methods should be employed that are refractory to them. A combination of rigorous source protection plus extraordinary source monitoring serve as sufficient multiple barriers for parasite protection.