red, white, blue and purple (plumbing, p.4)

A closer look at the rough plumbing. A normal house would have one set of big PVC pipes for waste, and two sets of smaller copper pipes for hot and cold water. What's different here? A few things...

There are two sets of drain pipes. As we've written earlier, the purple PVC pipes take water from the bathtubs and showers to a graywater filtration tank. That water is then supplied to the toilets through smaller cross-linked polyethylene (PEX) tubing, also colored purple, like the tube in the center of this photograph. The white PVC pipes drain to the septic system outside. The color coding helps ensure that we avoid contamination of the different systems.

The cold and hot water are supplied by PEX tubing colored blue and red, respectively. The PEX tubing is flexible, which eliminates the soldered elbow connections in a copper tube system (a common source of failure). PEX is also cheaper, and has a smaller environmental footprint, than copper, so it is preferred by sustainability ratings systems like LEED.