Effects of Relaxed Minimum Pipe Diameters on Fire Flow, Cost, and Water Quality Indicators in Drinking Water Distribution Networks

The use of pipes no smaller than 150 mm (6 in.) in diameter is often recommended for fire protection in North America. This work examines the some of the costs and benefits of this restriction by looking at a single pipe in isolation. First, we argue that North American fire flow requirements are quite conservative by international standards, with European requirements approximately 25% of those in North America. It is shown that smoother 100-mm PVC in place of older, rougher 150-mm cast iron can produce 60% of the available fire flow, in principle still exceeding the European requirement. Furthermore, the estimated capital cost is reduced by 30%, and water age by 56%. No differences in energy use were observed, owing to very low demands in normal service. A simple model of biological growth showed some potential for increased biological growth in smaller pipes, however. Smaller pipes likely have more dynamic shear stresses, which can mitigate discoloration. Overall, there may be many benefits if smaller-diameter pipes are permitted in low-density suburban service. Fundamentally, the amount of water needed to fight modern fires in North America is largely unknown, suggesting a need for additional research.