Assessing the health consequences of deficiencies in water distribution networks: a basis for future network management

Licentiate thesis, 2018

Drinking water distribution networks are susceptible to incidents that may contaminate the drinking water being served to the population. Five major risks that can impact negatively the health of consumers have been identified by a literature study: intrusion, cross-connections and backflows, unhygienic repairs or maintenance works, inadequate management of storage reservoirs and biofilms. All of them have been linked to outbreaks of waterborne disease, in addition to possibly increasing the level of endemic gastrointestinal illness in society.

There are two ways to determine the association between incidents in the network and risk for disease: epidemiological studies and modelling. Epidemiological studies have been used to assess the health outcomes to certain exposures in the network, e.g., maintenance work, low pressure events, among others. Studies have linked substantially outbreaks to causes in the network; however, the association with endemic level of disease in the population has had mixed results. Quantitative microbial risk assessment (QMRA) is one of the best frameworks available to simulate the health risks these incidents have on the population.

In this thesis, the foundations for a distribution network microbial risk management framework is established. This is achieved with a systematic literature review and the development of a conceptual model, specifically for the risk of cross-connections and backflows. The systematic literature review was carried out to assess the level of epidemiological evidence for endemic disease, and evaluate the state-of-the-art of QMRA models. A conceptual model for the specific risk of cross-connections and backflows is presented, testing some scenarios to gain insights for future improvements.

Possible improvements for QMRA models, better input data and combination of modelling and epidemiological studies are discussed. One important limitation that needs to be addressed is the economic aspect of potential mitigation measures for incidents. This aspect, in conjunction with the ones previously mentioned, will be essential to overcome in order to have a functional microbial risk management framework.