Integrated and Probabilistic Risk Analysis of Drinking Water Systems

Licentiate thesis, 2008

Drinking water supply is an essential public function but is at the same time exposed to risks. Since a totally risk-free society is not attainable, risks need to be managed efficiently to achieve an acceptable level of risk. A reliable supply of safe drinking water is vital and the World Health Organization emphasises an integrated risk management approach, including the entire drinking water system from source to tap. An integrated approach is important as there are interactions between different parts of a system. Efficient risk management requires appropriate risk analyses to characterise risk and support decision-making. Risk analysis based on an integrated approach facilitates well-informed decision-making and efficient use of resources for risk reduction. However, guidance on methods for integrated risk analysis of drinking water systems is limited. To support risk management of drinking water systems, a method for integrated and probabilistic risk analysis has been developed and evaluated based on a real-world application. The method is probabilistic in order to include uncertainties of estimates, which always exist due to lack of knowledge and natural variation. A framework for integrated risk management of drinking water systems is also suggested to show the context for risk analysis and to point out important steps in risk management of drinking water systems. The suggested method can be used to model entire systems from source to tap and to include interactions between events. It provides information on risk levels as well as the dynamic behaviour of the system in terms of the failure rate and duration of failures. Furthermore, it enables comparisons of the results with performance targets and acceptable levels of risk. One single method cannot be used to handle all risk-related issues. What is needed instead is a set of tools. The method developed has been shown to facilitate integrated risk analysis from source to tap and thus also informed decision-making, which may assist in minimising sub-optimisation of risk-reduction options. The method is thus one source of input into a set of tools to assist water utilities in risk analysis and risk management.