Evaluation of treatment methods to reduce the corrosivity of soft waters

Soft waters characterised with low alkalinity tend to reduce the lifetime of pipes in drinking water distribution systems. Consequently, the corrosion induced is likely to deteriorate water quality at the consumer's tap. Two different types of treatment methods are commonly used to control the corrosion effects of soft waters: (i) the addition of phosphate corrosion inhibitors, and (ii) the remineralisation process. In order to facilitate the decision making of network operator to use suitable treatment methods, a comparative pilot-scale experiment was performed. The above two treatment strategies were tested using pipes representing both drinking water distribution systems (used materials: cast iron and steel) and household plumbing systems (used material: copper). The impact of the two techniques was assessed by means of water quality monitoring (pH, metal leaching, etc) and of corrosion measurements using electrochemical probes as well as weight-loss coupons. The results obtained after a 15 month long experiment showed that remineralisation method was clearly the most effective way to control soft water corrosion. The implementation of this method resulted in a 50% reduction in metals leaching and about 40% decrease in iron corrosion rates.