The Topeka Capital-Journal recently published a story on the large number of water main breaks that the city has endured in recent years. Topeka’s water system relies on 870 miles of pipe. Since the 1940s, Topeka has diversified its system by adding ductile iron pipe and polyvinyl chloride (PVC) pipe. Today, the system is 39% cast iron pipe, 27% ductile iron pipe, and 25% PVC pipe (figure 1).
Percentage of Pipe Materials Used
Of the city’s water main breaks, approximately 66.8% were from cast iron pipes, 18.4% were from ductile iron pipes, and a mere 4.5% were from PVC pipes (figure 2).
Percentage of Pipe Breaks by Material
In Topeka, all iron pipes have a failure rate that is more than 18x the failure rate of PVC (figure 3). Ductile iron pipe devotees (and their lobbyists) will tell you that ductile iron is a great improvement over cast iron. And yet, ductile iron pipe still fails at more than 4x the rate of PVC pipe (figure 4).
Pipe Breaks: Iron V. PVC (%)
Pipe Breaks: Ductile Iron v. PVC (%)
In fact, Topeka has seen a significant number of ductile iron pipes grossly underperforming their expected life span:
The ductile iron pipe industry wants the public to believe that its product is more reliable than PVC but the facts show otherwise. As demonstrated by this case study, PVC is clearly the more durable material.