Fuzzy Logic Methodology
Safe drinking water does not mean there is zero risk associated with drinking water supplies. "Safe" is not an absolute, but a relative condition, and the practical indication of safe water is water at a level of risk that is so small that water consumers do not need to worry about getting sick from the water, or the risk is 'de minimus'.
The risk of failure in a water supply system is usually expressed in qualitative terms rather than quantitative terms. This occurs because there is substantial difficulty in identifying frequencies for many of the risk factors of drinking water supply failure due to the lack of data; as a result, fuzzy logic methodology provides an effective procedure to formalize a search for the potential risks of failure of a drinking water supply system. However, because the ranking process of likelihoods and consequences of failure/risk factors still relies on necessary levels of information, the decision-making of rankings is not simple and straightforward; it requires considerable knowledge of a specific system.
The fuzzy logic procedure allows identification of which failure items contribute to the high potential risk of the drinking water quality failure and to public health concerns, which assists managers and operators of water utilities in identifying problems and ensuring safe water for its consumers.
The case study of the cryptosporidiosis outbreak in North Battleford shows that waterborne outbreaks may occur and/or be investigated using multiple factors and the fuzzy logic approach assesses the importance of causative factors. The model is used to assess the robustness of multiple barrier designs for water supply systems indicating that while the aggregate risk is important, the percentage of risk in the high scales can be evaluated most effectively when the number of categorized risk scales is small.
References
This article was written by Edward McBean and was adapted from his paper, Fuzzy-Logic Modeling of Risk Assessment for a Small Drinking-Water Supply System, published by ASCE.
