In every state, the legal and most common sources of greywater are the showers, tubs, bathroom sinks, and clothes washer. These sources account for over half of all the water used inside a residence. Other legal sources of greywater are the tail water from non-salt generating water conditioners, Jacuzzis, and utility basins, basically anything but kitchen and toilet water.

The most cost effective sources to include in the greywater pipeline are the regularly used showers, tubs, and clothes washer, though reverse osmosis systems waste a lot of very good water that can be used in our systems. While you may have 8 bathrooms in your home, if only 3 of them are producing greywater on a regular bases, it may not be cost effective to dual-plumb all the extra sources. If one of your extra bathrooms receives guests more often than the others extra bathrooms, it might pay to include that extra shower/tub. If your home is in the middle of the desert, relying on well water, then plumbing every legal source is probably cost effective for you.

NOTE: It is always more cost effective to state on your original plumbing bid that you want certain drains separated into a greywater main line, with that mainline taken to where you want the ReWater filter system to sit, and that ReWater filter system to be attached to that mainline and to the sewer line via an overflow, and that you’ll need at least a 1″ high pressure fresh water line brought to that filter system for filter backwashing. If you do not state all this on your original plumbing plan, you will later be charged for a “change order” by your plumber, and the exact same work will cost you many times more than it would have cost if you had included it on your original plan.

Whatever wastewater code you use locally determines the mechanical composition of the plumbing to and from the greywater system itself. If you’re in California, you will use the California Plumbing Code (CPC), which is based on the Uniform Plumbing Code. For the greywater system itself, note that the CPC is different from the UPC. (The UPC does not specifically allow underground drip systems) In most western states, the UPC is the governing code for the plumbing, but there may be a local amendment to that code.

You must install a reduced pressure principle device (RP device) on the fresh water pipe that supplies water to the filter system. This water is used to backwash the filter media and to provide supplemental water to the irrigation system, should there not be enough greywater to fulfill the entire irrigation schedule on any given day. Without the RP device, there is a chance of greywater contacting your fresh water supply in the event of a major upstream water supply disruption that causes a reverse flow in your water lines.

plumbing-1This picture shows a vent for the greywater surge tank to the roof being installed in a future wall before the foundation is poured. If the tank sits within 10′ of an openable window or door, it needs to be vented through the roof. It can connect to any vent stack.

If you can not reach the vent stack, you can use a “wet vent” by installing over-sized piping for your greywater supply line from an existing vent to the tank.

If the tank does not sit within 10′ of an openable window or door, it can use a simple “candy cane” vent.

This picture is a bird’s eye view of a surge tank (on the left) and all the “outside the house” plumbing leading around a concrete step to a filter vessel location (without the filter attached).

Note the copper pipe carrying fresh water for backwashing the filter, as well as the pump discharge pipe, and a filter discharge riser going to the sewer, and an irrigation mainline, all in the same trench. These pipes can be either black ABS or white PVC. Displacing a filter from the surge tank requires extending all those pipes (and some wiring too).

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