A number of approaches offer promise for addressing the limitations of current antibody‐based detection methods. This report was prepared by the Working Group on Waterborne Cryptosporidiosis (Technical Task Force E, Developmental Status of Environmental Sampling, Water Testing, and Surrogate Indicators). Methods for detecting Cryptosporidium oocysts in water have centered around microscopic examination of fluorescent antibody‐stained concentrates from large‐volume water samples. The limitations of these antibody‐based methods include the need for experienced analysts, lengthy analytical time, expense, lack of specificity, erratic efficiency, low precision, and difficulty in determining viability. A number of methods, assays, and procedures that have the potential for ameliorating some of these limitations are currently being evaluated. How successful such processes will be remains to be demonstrated by the scientific community.

New York City is making every effort to protect its watershed to assure water quality and maintain filtration avoidance. Since 1987, New York City has enhanced its comprehensive watershed monitoring program (including pathogen monitoring), developed a disease surveillance and outbreak detection program, and implemented a watershed protection program that has improved water quality. The city recognized that high‐quality source water and effective watershed protection are the foundation of filtration avoidance under the federal Surface Water Treatment Rule (SWTR). Accordingly, the city applied for and received filtration avoidance determinations for the Catskill and Delaware portions of its system. This article summarizes the city's water quality data and watershed monitoring and protection programs in the context of the SWTR. A Watershed Memorandum of Agreement, signed Jan. 21, 1997, provides for land acquisition, updated watershed regulations, and partnership programs. As part of the watershed agreement, USEPA issued a four‐month interim filtration avoidance and will issue a revised filtration avoidance later in 1997. Provided the city meets certain provisions, this will allow it to avoid filtering the Catskill and Delaware supplies until at least Apr. 15, 2002.

A study was carried out to determine the degree of biological activity in the drinking water supplied to New York City by the Croton and Catskill/Delaware systems, as measured by the Attached Growth Rate Estimate (AGRE) method. Also, possible relationships between AGRE results and standard water quality parameters were examined. The AGRE results for both the systems ranged between 0 and 0.5 d−1, indicative of biologically stable water. These results suggest that excessive bacterial growth in the New York City distribution system would be rare. The Croton results were temperature and alkalinity dependent. The Catskill/Delaware results revealed that growth rates decreased with travel time in the distribution system. These differences emphasize the complexity of biological activity monitoring in drinking water distribution systems.

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