Fault tree analysis for integrated and probabilistic risk analysis of drinking water systems

• Published in: Water research (Oxford) Vol. 43; no. 6; pp. 1641 - 1653
• Main Authors: Lindhe, Andreas, Rosén, Lars, Norberg, Tommy, Bergstedt, Olof
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.04.2009; Elsevier
• Subjects: Applied sciences; Civil Engineering; consumers; Customer Minutes Lost; drinking water; Drinking water system; Environmental Monitoring - methods; estimation; Exact sciences and technology; Fault tree; hydrologic models; Integrated; Models, Biological; Monte Carlo Method; Oceanografi, hydrologi, vattenresurser; Oceanography, Hydrology, Water Resources; Other industrial wastes. Sewage sludge; Pollution; Probabilistic; probabilistic models; Probability; Probability Theory and Statistics; Reproducibility of Results; Risk analysis; Risk Assessment; Samhällsbyggnadsteknik; Sannolikhetsteori och statistik; simulation models; Sweden; Uncertainties; Wastes; Water Microbiology - standards; Water Purification - standards; water quality standards; water supply; Water Supply - standards; Water treatment and pollution; Sweden; Europe; Fault tree; Drinking water system; Probabilistic; Customer Minutes Lost; Risk analysis; Uncertainties; Integrated; Drinking water; Monte Carlo method; Uncertainty; Water quality standard; Modeling; Optimization; Risk assessment
• ISSN: 0043-1354; 1879-2448; 1879-2448
• DOI: 10.1016/j.watres.2008.12.034

Drinking water systems are vulnerable and subject to a wide range of risks. To avoid sub-optimisation of risk-reduction options, risk analyses need to include the entire drinking water system, from source to tap. Such an integrated approach demands tools that are able to model interactions between different events. Fault tree analysis is a risk estimation tool with the ability to model interactions between events. Using fault tree analysis on an integrated level, a probabilistic risk analysis of a large drinking water system in Sweden was carried out. The primary aims of the study were: (1) to develop a method for integrated and probabilistic risk analysis of entire drinking water systems; and (2) to evaluate the applicability of Customer Minutes Lost (CML) as a measure of risk. The analysis included situations where no water is delivered to the consumer (quantity failure) and situations where water is delivered but does not comply with water quality standards (quality failure). Hard data as well as expert judgements were used to estimate probabilities of events and uncertainties in the estimates. The calculations were performed using Monte Carlo simulations. CML is shown to be a useful measure of risks associated with drinking water systems. The method presented provides information on risk levels, probabilities of failure, failure rates and downtimes of the system. This information is available for the entire system as well as its different sub-systems. Furthermore, the method enables comparison of the results with performance targets and acceptable levels of risk. The method thus facilitates integrated risk analysis and consequently helps decision-makers to minimise sub-optimisation of risk-reduction options.