Underground water mains are pipes that supply safe drinking water—the lifeblood of society–to millions of consumers. Most who benefit from this service seldom consider the vast water delivery network below their feet—until something goes wrong. Water main breaks may exact considerable social and economic costs, including property damage, risks to public health, increased water utility fees, traffic disruption and public endangerment (see video).
The 2012 American Water Works Association report, Buried No Longer: Confronting America’s Water Infrastructure Challenge warns that much of our drinking water infrastructure is nearing the end of its useful life and requires replacing; in some high-growth regions larger networks are required to provide water services. A recent Utah State University survey of US and Canadian utilities sheds light on current pipe inventories and failure rates of various pipe materials in the period 2010 to 2011. The survey data are reported in the October, 2012 issue of the Journal of the American Water Works Association and are intended to represent a benchmark for utilities as they make decisions on repairing and replacing the pipes that deliver clean water to their customers.
Based on the survey results, the primary pipe materials in use in the US are cast iron (28 percent), ductile iron (28 percent) and polyvinyl chloride (23 percent); other pipe materials used are concrete pressure pipe, steel, asbestos-cement, and polyethylene. Pipe material varies by region, with cast and ductile iron dominating in the Northeast and Great Lakes areas and polyvinyl chloride common through the West and South. Polyvinyl chloride is the leading material in use in Canada.
Currently polyvinyl chloride pipe has the lowest overall failure rate, calculated as the number of failures per 100 miles of pipe per year. Cast iron is the pipe material identified as failing most often, probably because it is one of the most commonly used materials and because it is on average the oldest pipe material in use.
Forty-three percent of installed pipes are between 20 and 50 years old, according to the survey data. Over 22 percent of installed pipe considered in the survey is greater than 50 years old and 8.4 percent of pipes were classified as “beyond their useful life.” Even though the average age of failing water main was found to be 47 years, survey respondents believed new pipe should last an average of 79 years. Over 77 percent of utilities surveyed reported they have a replacement plan for water mains that are nearing the end of their useful life.
Rounding out the Conversation about Water Infrastructure
Water mains represent some of our most essential but hidden infrastructure. According to the survey data, an average of approximately 264 people are served per mile of water main in urban and rural areas of North America. Factoring in national population data, the researchers conclude there are approximately 1.18 million miles of water mains in the US and over 8,000 miles of water mains in Canada.
The AWWA report estimates the price tag for US water infrastructure renewal is a whopping $1 trillion. It is time, as that report notes, to bring the conversation about our aging water infrastructure above ground. With valuable data on pipe construction and age, the new Utah State University survey helps do just that.
Fred Reiff, P.E., is a retired official of the Pan American Health Organization and the U.S. Public Health Service.