A Framework for Applying the Precautionary Principle to Drinking Water Disinfection Policy and Decisionmaking

The Precautionary Principle requires that in the absence of scientific consensus on a potential risk, a policy or action should err on the side of caution to protect public and environmental health. The principle has been successfully applied to guide chemicals policy in the European Union, however its applicability in other settings is not always straightforward. Drinking water treatment and disinfection are critical for the protection of public health from waterborne infectious diseases and to minimize exposure to metals and other contaminants present in source water. However the processes to treat and disinfect water may result in increased risk of other health outcomes; for example, there is relative scientific consensus that bladder cancer is associated with exposure to trihalomethanes, which may be formed during disinfection with chlorine. There is less certain evidence of the potential adverse effects when treatment processes are altered to reduce trihalomethane formation. Chloramination and ozone create different disinfection byproducts such as n-Nitrosodimethylamine, bromate and aldehydes. Compared to the understanding of risk from exposure to trihalomethanes, there is considerably more uncertainty surrounding the potential health impacts of exposure to these other disinfection byproducts, alone and in mixtures. In this presentation, I will describe how drinking water treatment and disinfection are consistent with the Precautionary Principle, and will propose a framework for applying precautionary policy to drinking water regulation and policy in the face of scientific uncertainty.