Modeling the Risk from Giardia and Viruses in Drinking Water

This article discusses the assessment of risk from microorganisms in drinking water, the problems associated with such an analysis, the approach for specific organisms, the monitoring required to demonstrate that risk levels are met, and how risk assessment might be approached for determining whether a given level of risk from Giardia and viruses is avoided. Guidelines are suggested for determining the level of treatment necessary to ensure that consumers receive a finished drinking water with risks of less than one infection per 10,000 people per year from Giardia and enteric viruses. There is a critical need for the practical application of quantitative assessments of risk from pathogens in drinking water. There are a number of questions that need to be addressed. Does a system really need to filter? What is an adequate watershed control program? How much disinfection, depending on the level of contamination in the source water, should a system that filters apply? When is the minimum 3and 4-log removal-inactivation requirement for Giardia and viruses, required under the Surface Water Treatment Rule (SWTR), not enough? When is disinfection warranted in a groundwater system? What level of disinfection should be provided? How much less disinfectant can safely be used in order to minimize risk from disinfectants and disinfection byproducts? Once practical modeling of risk from pathogens in drinking water is available to the industry, it should be possible to answer these questions more readily. This article discusses the need for risk assessment for microorganisms, the problems associated with such an analysis, the approach for specific organisms, the monitoring required to demonstrate that risk levels for specific organisms are met, and how risk assessment might be practically Introduction by Kenneth L. Mercer, Editor-in-Chief