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Experiences with Watermain Corrosion

Published: 19880503 by American Waterworks Association
Author(s): Robert Gummow

The cost of rehabilitating the 38,000 km of water distribution piping in Ontario, currently valued at $21.2 billion ($2,725 per capita) has become a major focus of attention. Not only is it estimated that 15% of the water supplied is unaccounted for but the average annual breaks per 100 km is an astounding 25 resulting in annual emergency repair costs estimated at $65 million.

The Ministry of Environment report of January 1987 entitled “The Need for a Rehabilitation Program for Water Distribution Systems in Ontario” further estimated that the annual cost for replacing Ontario’s water system would be $50 million assuming only 50% required reconstruction over the next 50 years. There is a major concern as to who will pay the cost of this rehabilitation since most current water rate charges are insufficient to provide replacement funding. Despite appeals for funding to all levels of government by the Ontario Sewer and Watermain Contractors Association, it is apparent that there is substantial resistance to these requests. Yet as the appeals for special funding echo through our industry, municipalities continue to repair about 9500 breaks annually with the expectation that this number will continue to grow. Environment Ministry estimates however that if the break frequency could be reduced to 10 breaks per 100 km, then an annual savings of $15 million would be realized.

The question then arises as to whether or not the “break” rate can be practicably reduced. Numerous studies have identified corrosion to be the primary cause of both grey cast iron and ductile iron watermain failures. Accordingly, if the corrosion activity can be reduced then the service life can be proportionately extended and the “break” rate reduced.