Predicted Public Health Consequences of Body‐contact Recreation ON A POTABLE WATER RESERVOIR

The Metropolitan Water District of Southern California recently completed construction of an 800,000 acre-ft (1 x 10 9 m 3 ) drinking water reservoir. Recreational activities, including swimming and other sports involving direct body contact (BC) with the water, have been the subject of considerable interest by local community members. Consequently, a modeling-based risk assessment study was conducted to assess the potential public health consequences to downstream potable water users consuming water from this reservoir if BC recreation was permitted. Results of the study indicated that the annual risk of waterborne illness would increase three times above background, despite conventional treatment. Moreover, the occurrence of high-loading pathogen events associated with BC recreation was observed to significantly increase the daily risk of waterborne illness to downstream consumers. The study also considered the cost of additional treatment that would be necessary to address the increased risk. The modeling approach used in this study provides guidance for policymakers and stakeholders who are examining issues associated with BC recreation and drinking water reservoirs.