The excessive use of water drawn from both surface and underground sources has led to a deficit in this precious resource. Various water-efficiency measures (e.g. low-flow fixtures, sensors, use of non-potable water for irrigation applications) in commercial buildings and homes can greatly reduce water waste, yielding lower sewage volumes, reduced energy use, and financial benefits.
Aside from specification of the above devices and practices, using certain materials for plumbing systems can also have a significant impact on water use. For example, high-density polyethylene (HDPE) pipe is manufactured by extrusion, which produces a very smooth interior surface that, in turn, provides exceptional hydraulic characteristics. The HDPE pipe surface prevents the biological or chemical constituent being carried from adhering to the pipe surface.
As an added benefit, HDPE pipes maintain these flow characteristics throughout their long life. Other types of materials can subject the pipe to deterioration of their inner surfaces—while these products begin service with interior walls nearly as smooth as polyethylene, corrosion, or the formation of scale, can cause degradation of their flow capacity and increase the costs to pump waater over the life of the system. On the other hand, plastic pipe’s ability to move water efficiently in potable applications remains virtually unchanged. Therefore, energy costs for pumping can remain consistent over the life of the system.
Additionally, the life cycle cost of HDPE pipe differs from other pipe materials since its fused joints mean an allowable water leakage of virtually zero, rather than the typical leakage rates of 10 to 20 percent for other types of pipe. The combination of HDPE pipe’s flexibility and the potential for leak-free joints allow for unique and cost-effective types of installation methods unobtainable by rigid systems relying upon other types of connections.
In residential applications, cross-linked polyethylene (PEX) pipe is effective for employing a manifold system for the indoor plumbing.1 Using PEX pipe, this system allows for multiple feed lines throughout the house, which means hot water can arrive more quickly to a sink or shower. The result is increased potential for significant water efficiency and savings.
A 2003 report by the American Water Works Association (AWWA) indicated 8.3 trillion L (2.2 trillion gal) of potable water is lost each year in the United States due to leaks and breaks in an increasingly aging infrastructure.2 A switch to plastic water pipes (including HDPE and/or polyvinyl chloride [PVC] products) could not only save much of the water currently being wasted, but could also greatly reduce the nearly $3 billion in annual lost revenue (cost of the lost water) experienced by water utilities.
The corrosion-resistance and durability of plastic water pipe can help make it an excellent alternative to other systems relying on traditional materials. A two-year study conducted by the National Research Council of Canada (NRC) found for each 100 km (62 mi) of water distribution pipe laid, PVC had only 0.7 annual breaks, compared with 35.9 and 9.5 for cast iron and ductile iron, respectively.3
Although the durability of PVC pipe allows it to last as much as 10 times longer than other materials, some manufacturers have shown their commitment to sustainability by participating in ‘take back’ programs.4
1 For more information on this system, see “Flexing your PEX—Plumbing the possibilities of cross-linked polyethylene pipes,” by Camille George Rubeiz, PE, in the November 2004 issue of Modern Materials.
2 See “Committee Report: Applying Worldwide BMPs in Water Loss Control” (AWWA Journal, August 2003).
3 See B. Rajani and S. McDonald’s National Research Council of Canada report, Water Main Break Data for Different Pipe Materials for 1992 and 1993.
4 The Uni-Bell PVC Pipe Association, a non-profit, research organization representing the North American gasket-joint PVC pipe industry, administers one such program. Visit www.uni-bell.org.