probability, and equity would make decisions impossible because stakeholders would weigh these components differently, and there are no obvious bright-line distinctions. However, the current decision paradigm considers some of the factors implicitly while ignoring others without any explicit attempt to set priorities, so it is hard to argue that better understanding of the implications of decisions would not be beneficial. A final critique could be that stakeholders are ultimately concerned with the decision rather than the method. If this approach resulted in a conclusion that building the power plant in the low-income community were the optimal solution, residents of the community would be unhappy; if this approach resulted in a decision not to build a new facility, the proponents of the power plant would be unhappy (even if the process and analysis were transparent and agreed on). That may be impossible to avoid, but upfront consideration of scoping and decision criteria will at least reassure stakeholders that the criteria were not determined post hoc, and the rationale for the decision will be clearly presented.

A CASE STUDY OF DECISION SUPPORT FOR DRINKING-WATER SYSTEMS

Decision-makers and stakeholders seeking safe drinking water carry out their work in the face of a daunting array of microbial, chemical, climatic, operational, security and financial hazards. The capacity of risk assessment to support the societal goal of the provision of safe drinking water is an example of the critical need to reorient current risk-assessment practices away from the support of a series of disconnected single-hazard standard-setting processes and toward the provision of analytic support to facilitate the integration of complex health, ecologic, engineering, and economic elements of decision-making involved in providing safe drinking water.

Risk-assessment activities that are directed toward the safety of drinking water primarily support standard-setting exercises. The setting of such standards does not represent the types of more concrete system-design risk-management decisions that have direct physical, biologic, and chemical impacts on the safety of drinking water, representing distal decisions with ambiguous connections to risk reduction rather than proximal decisions with clear causal connections to risk reduction.

It is now generally understood that drinking water is best protected by an integrated risk-management approach in which multiple barriers are applied to protect against exposure to the hazards. The intervention options for drinking-water risk management include a complex set of decisions that affect system components that include sewage treatment, source-water selection and protection, multiple stages of water treatment, investments in operator training and information-management systems, changes in laboratory and monitoring practices, protection of the water in the distribution system, household water-use practices, and the capacity for effective emergency response that needs to be engaged when other barriers fail. It is inevitably a complex design problem to reduce risk from multiple sources that are subject to numerous competing constraints. The constraints include the fact that reducing some risks can increase others (the now classic problem of toxicity from disinfection byproducts that are produced in some processes aimed at reducing microbial risks or in choosing among sources of raw water that have varied microbial and chemical risk profiles). Other constraints include financial resources available in the short term and long term, the political and economic implications of issuing boil-water advisories, and the need to provide adequate protection to highly susceptible sub-populations (for example, in the case of persons with HIV/AIDS and the risk of cryptosporidiosis).

The societal goal is ultimately not to set standards themselves but rather to minimize the net risk associated with the provision of drinking water given the aforementioned risks



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