Thoroughly Purple PVC Pipe Keeps Recycled Water from Being Used for Drinking

EASTLAKE, Calif., Oct. 16, 2007 (VNS) – Seventeen stores at a local business center discovered this summer that recycled—not drinking-quality—water was flowing through their taps. The root cause was that the pipes carrying the water were not really purple, which is the designated color for pipes carrying recycled or reclaimed water.

The pipe was copper, with a purple plastic sleeve. The local water district reported that when the pipe was installed, the sleeve had somehow slipped below ground, so whoever hooked the pipe to the water meter did not realize it carried reclaimed water.

“An error like that couldn’t happen with PVC pipe where the color is built into and permeates the product,” said Craig Fisher, technical director of Dallas-based Uni-Bell PVC Pipe Association.  He added that PVC is the most widely used purple pipe material today, and demand is rising steeply as water supply and conservation issues become more critical, particularly in the West and South.

Aside from being purple through and through, Fisher said that PVC pipe for reclaimed water has a smooth inner surface that does not offer a haven for the bacteria to breed. Also the pipe material does not have nutrients for bacteria to feed on. 

“That means there’s less chance of producing bio-film (also known as slime),” he said. “As a result, PVC pipe is easier to maintain.”

Fisher explained that the water leaving the treatment plant contains residual disinfectant that is supposed to deal with any slime encountered in the pipes. But if there’s a lot of slime, the residual disinfectant is used up before the water reaches its final destination. In PVC pipes, the residual disinfectant remains intact for the entire trip.

Reclaimed water is wastewater that has been treated at a sewage treatment plant to the point of being safe for body contact, if not for drinking. It is currently used to irrigate crops and water golf courses and municipal green spaces. California is working on legislation to change the state plumbing code to require dual piping systems in institutional, industrial, and office buildings so that reclaimed water supplies, when available, can be used outdoors for watering landscape and indoors for flushing toilets.