Risk-Based Decision Model for Microbial Risk Mitigation in Drinking Water Systems
Doctoral thesis, 2019

Microbial risks in drinking water systems can cause sporadic pathogenic infections and waterborne outbreaks resulting in large costs for society. In 2010 for example, around 27,000 persons were infected with Cryptosporidium in Östersund, Sweden. It is so far the largest waterborne outbreak in Europe, and societal costs were estimated at SEK 220 million (approx. 20 million €). To achieve a safe drinking water supply, assessment of microbial risks and, when needed, implementation of risk mitigation measures is necessary. However, drinking water systems are complex, and risk mitigation measures are expensive. A thorough evaluation of possible mitigation measures is thus essential for identification of the most suitable alternative and efficient use of societal resources. In this thesis, a risk-based decision model for evaluating and comparing microbial risk mitigation measures in drinking water systems is presented and illustrated using two Swedish case studies. The decision model combines quantitative microbial risk assessment and cost-benefit analysis in order to evaluate decision alternatives from the perspective of social profitability. The quantitative microbial risk assessment is complemented with water quality modelling and consideration of unexpected risk events, such as extreme weather events and combined sewer overflows, in order to reflex the complexity of drinking water systems. To facilitate transparent cost-benefit analyses, the effect of different health valuation methods on the output from the decision model is presented. In the decision model, health benefits and other benefits are monetised for each mitigation measure and compared to the costs for implementing the measure. It is possible to combine decision criteria such as tolerable risk levels and maximising the net present value when applying the decision model. The decision model integrates several scientific disciplines, thus constituting a novel approach to evaluate microbial risk mitigation measures in drinking water systems and provides a structured analysis that includes often neglected aspects. The model provides transparent and holistic decision support and facilitates well-founded decisions balancing risks, costs and societal benefits.

drinking water

quantitative microbial risk assessment

cost-benefit analysis

health risk

contaminant fate and transport modelling

economic valuation of health effects


SB-H4, Sven Hultins gata 6
Opponent: Sarah Dorner, Polytechnique Montreal, Canada


Viktor Bergion

Chalmers, Architecture and Civil Engineering, Geology and Geotechnics

V. Bergion, V., Lindhe, A., Sokolova, E. and Rosén, L. Accounting for unexpected risk events in drinking water systems

Water is essential for human wellbeing. We need it, among other things, for sanitation, food and drinking water. The drinking water comes mainly from either surface water or groundwater sources and is typically treated before being distributed to the consumers. The lack of proper treatment or failures may result in pathogens, originating from wastewater or other sources, being spread through the drinking water system and thus posing a risk to drinking water consumers.

Waterborne pathogens can cause gastrointestinal disease, and the costs to society in terms of human suffering, healthcare costs, loss of production, etc. could be substantial, especially in the case of a larger waterborne outbreak. To provide safe drinking water, the entire supply system, from catchment to consumer, must be considered. If the risk level is too high, risk mitigation measures are required. These mitigation measures are often expensive, and the decision on how to choose the most suitable measure must be made using a holistic approach.

In this thesis a decision model is presented. The decision model supports drinking water producers in their evaluation of microbial risk mitigation measures, and acts as an aid when choosing the alternative that is most beneficial to society. The novelty of the decision model lies in the combination of several different methods to describe the transport routes of pathogens in drinking water systems. The model is also novel in integration of multiple scientific fields to enable a thorough evaluation of microbial risk mitigation measures considering societal benefit and profitability.

Driving Forces

Sustainable development

Subject Categories

Civil Engineering

Water Engineering

Other Earth and Related Environmental Sciences

Earth and Related Environmental Sciences



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4649



SB-H4, Sven Hultins gata 6

Opponent: Sarah Dorner, Polytechnique Montreal, Canada

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