The Occurrence and Significance of Corrosion Deposits in Drinking Water Distribution Systems.

A major challenge for the management of drinking water distribution systems is to minimise the occurrence of red water, which arises predominantly from the corrosion of iron water mains. This research adopts a novel approach by focusing on the product of the corrosion process i.e. corrosion deposits. A fundamental study of the nature and occurrence of corrosion deposits and their role in red water generation was undertaken to improve knowledge on managing ageing distribution systems. The nature of corrosion deposits was characterised by field surveys in Thames Water’s Distribution System. The chemical composition of deposits was found to be similar across the network. However, the occurrence of deposits was highly variable, even along the same stretch of main, which highlighted the influence of localised pipeline features, such as joints. Corrosion deposits were postulated to effect red water by providing a physical barrier and being composed of unstable minerals which promote red water generation. Experimental modelling on a pilot-scale distribution system, found no evidence to link certain minerals (eg Lepidocrocite) with red water. There was more evidence to support the physical role, with the formation of stable deposits associated with the cessation of red water and the return of red water associated with the physical disruption of the deposit structure. The overlying water quality was observed to effect this relationship, with elevated temperatures (>20C) and anaerobic conditions associated with red water generation in the first three months of the experiments. This study found that the role of the nature of the corrosion deposits on the potential for red water generation superseded that of changes in water quality over time. Continuous monitoring demonstrated the generation of red water at times of no flow; attributed to a mechanism known as iron uptake. These studies highlighted the potential significant contribution of iron uptake to red water generation in null flow points in distribution systems