Forensics of water quality failure in distribution systems - a conceptual framework

Precise causes of water quality failures are often difficult to pinpoint. The complexity of the distribution system (many kilometers of pipes of different materials and ages), occurrences of physical/chemical/biological processes and the lack or absence of timely data make forensic analyses of water quality failure events very challenging. Water quality failure in the distribution system can occur through several pathways. These include intrusion of contaminants through failed or compromised pipes and cross-connections, regrowth of microbes in pipes and distribution storage tanks, leaching of chemicals or corrosion products from system components (pipes, tanks, liners), water treatment failure, deliberate contamination by terrorists and permeation of organic compounds through various plastic components of the system. Various indicators of water quality failure (symptoms) such as changes in the turbidity, odour, taste and colour, waterborne illnesses ranging from minor to serious, etc. can provide clues as to the causes of the failure in much the same way as symptoms of human health are used to diagnose causes and propose treatment. A framework is proposed using fuzzy-based techniques and a knowledgebase on water quality. This framework is capable of backtracking symptoms to determine the candidate categories of contaminants, sources and/or pathways that cause a given water quality failure and rank them according to their respective likelihoods (or memberships). The usability of the framework is demonstrated with the help of a hypothetical case study.