Picking the Right Pipes

A reader asks the Green Guide:
With regards to your alternatives to rigid PVC pipe and suggesting it shouldn't be installed in homes due to its environmental factors, what else could be used? You mentioned cast iron or steel pipe, but don't the methods by which steel and cast iron pipes are produced (and extracted from the earth) generate enormous amounts of emissions? It seems like all solutions are imperfect, but we do need water transport lines...so what can we do?

The Green Guide responds:
When you start analyzing the lifecycle of each material available to supply and drain water from our homes, it's hard to choose a clear winner. While pipes made from high-density polyethylene (HDPE) and cross-linked polyethylene (PEX) seem to have an edge over their competitors based on the smaller impact of their production and their versatility, you shouldn't write off tried-and-true materials, such as copper, which may prove more appropriate for your specific needs.

To answer your question more specifically though, pipes made of metal, whether copper, iron or steel, take an enormous amount of energy to produce, and metal mining generates large quantities of solid and chemical waste. In fact, it has earned the reputation of being this country's most polluting industry. Despite all this, a lifecycle study done by Environment Canada found that metal pipes still had less of an environmental impact than polyvinyl chloride (PVC) piping, the production of which is known to release dioxin, a carcinogenic agent that may also cause reproductive disorders. It also releases toxic chemicals when burned and is made from non-renewable resources.

But in terms of durability, each of these materials (copper, steel, iron, PVC, HDPE and PEX) will last decades if properly designed and installed, according to the Environment Canada study. So your choice should ultimately depend on how much you're willing to spend, what specific purpose the pipe will serve (as a supply line or a waste line) and what's available in your area.

Copper is still the standard supply pipe of choice among plumbers. It does not corrode as quickly as iron or galvanized steel, and it won't interact with water, though elements in the water, such as chlorine, may cause leaching. (Too much copper can be dangerous, but many home water filters can remove it.)

The use of steel pipes has declined over the years due to its propensity to corrode from the inside, cutting water pressure to a mere trickle. But iron is still popular as both a supply and a waste pipe, as it withstands higher pressures than PVC. Although larger cast iron waste pipes can corrode (though at a much slower rate than steel) and eventually crack, this can be prevented by coating the interior with enamel or tar.

HDPE and PEX aren't as widely available but are growing in popularity as both supply and waste pipes, and PEX has a slight advantage over HDPE as a supply pipe since it withstands higher temperatures. Because they can be fused together by melting or welding, HDPE and PEX have been found to spring fewer leaks than PVC, which needs joints to connect the pipes.

If you must go with PVC, consider using it only for waste pipes, which increase in size as they run from each appliance to the sewer drain. For example, bathroom and kitchen sinks typically drain through one-and-a-half- or two-inch pipes, while the sewer pipe may be four to six inches in diameter, and those pipes have to fit together. PVC pipes fit together easily, since all you need is joints, couplings and cement; connecting metal pipes with threads can prove more time-consuming and awkward. Use less-toxic PVC glue instead of the more hazardous, but common, solvent-based cement (Gorilla PVC Glue, $6.95; www.ecowise.com).

A note about cost: Keep in mind that the price of materials isn't the only cost you should weigh when choosing pipes. Depending on your home's site and design and local labor costs, a cheaper material may be very expensive to install, and vice versa. The Environment Canada survey of the materials mentioned above found that all were comparable to PVC in terms of their total overall cost.