The New York City Department of Environmental Protection (DEP), the agency responsible for providing water for some eight million people, made application in November 1991 to the New York State Department of Health (DOH) for avoidance of filtration of its Catskill/Delaware supply under the Surface Water Treatment Rule (SWTR). One month later, the DOH granted conditional avoidance. When it evolved that the DOH did not have primacy, and that the US Environmental Protection Agency (EPA) would be obliged to make the decision, EPA assembled an Expert Panel to advise as to whether the city met the criteria for avoidance. The panel believes that, even with filtration, the more the source water is degraded, the greater the risk from disinfection byproducts and the greater the risks of the oocysts of Cryptosporidium getting through. Without filtration, given the level of development that already exists and with no capacity to restrict further development, the city is now and will in the future be at high risk. Both watershed protection and filtration are necessary in New York.