Epidemiologic impact of water reuse in Los Angeles County

The importance of recycled wastewater in the pathogenesis of disease has been considered in an ecologic analysis of four geographic areas of Los Angeles County. Two of the areas received recycled wastewater via the groundwater since 1962, while two similar areas served as controls. Of 19 health outcomes included in the analyses, five exhibited statistically significant differences among four areas. In none of these five analyses, however, were the differences in accord with the biologic hypothesis that recycled water causes disease. For only one outcome, deaths due to cancer of the rectum, were differences noted in which the high recycled water area had more excess deaths than the low recycled water area, and both had more excess deaths than the control areas. This positive association was of a low order, however, and might well have been due to chance (P = 0.08). The results of this first stage of our investigation suggest that as of 1969–1971, there were no grossly apparent adverse health effects associated with the use of recycled water. Nonetheless, a cautious interpretation of the study findings is necessary due to the inherent limitations of this type of analysis.