Drain water from your sinks, bathtubs, showers and washing machines have been given the term “graywater”, separating it from “blackwater” which is the term used for waste water from sewage systems. This can vary from one locality to the next some treat drainage water from sinks and tubs the same as sewage waste if it contains a high enough concentration of organic waste.
Graywater can be diverted with ancillary drain systems to be used as irrigation water, thereby recycling the water after it served one purpose and using it for another, reducing our demand on fresh water supplies. Usually graywater is filtered and used for supplying subsurface irrigation to plants that are not intended for human consumption, like decorative landscape plants. The high concentration of nitrogen and phosphorus are an added benefit to the plants nutrients and conserves treated tap water that can best be spent on quenching human thirst since even filtered graywater is not safe to drink.
Water systems utilizing graywater use the same basic traps and vents as your standard drain-waste vent, the difference is that the drains from the fixtures terminate in an irrigation line and not in a sewage line. There is more to installing a diversion system than just running separate lines of PVC pipe into a irrigation field, graywater must pass through a filtration system otherwise it quickly becomes a breeding ground bacteria and photogenes. It requires a holding tank to store the rapid influx of water used inside the home and since graywater is not pressurized like tap water it needs a pump to push the water through the irrigation lines. It may be necessary to install a diversion valve that allows the water to empty into the standard waste removal lines when needed, because although graywater is a valuable resource for recycling water, not all states allow it due to their safety regulations and if they do, some may require a permit. Dispensing graywater under the root level of the soil or the utilization of graywater near the vicinity of a domestic well may be prohibited, so check with your local health department before installing a diversion system.
It’s a good idea to include a three-way diversion valve and a graywater pump and filter to your system. In the event of a back up, blockage or plug in the system a three-way diversion valve can be divert graywater into the sewage collection system or an onsite treatment and disposal system saving you form additional stress and expensive repairs. If your local code allows, install a surge tank, pump and filter to your lines, you can build your own using a pump and a sand commonly found in swimming pools, be sure to house them in a concrete or metal structure that is large enough to give you easy access to parts during inspection, operation and maintenance of the system. A corrugated galvanized steel culvert about 8-12 feet makes an ideal housing unit.
