Whether simple or complex, there are a few key concepts of prime importance in designing any graywater system:
The core of most graywater systems is the three-way diverter valve, also called an L-Port valve, swivel ell, or changeover device. Water comes in one port, turn the handle one way to direct water out to the landscape, or turn it the other way to direct it to the sewer.
It’s important to be able to switch back to the sewer readily and easily, for example when washing diapers or shop rags, or when using bleach.
A simpler option for a laundry to landscape (L2L) system is to install a second standpipe that leads out to the yard beside the existing sewer outlet behind your washer. Just lift the washer outflow pipe by hand from one and move it to the other. See how Brad Lancaster does it at his home in Tuscon.
The main point is for it to be easy and obvious.
If you’re installing a valve, the best option for laundry is a 1-inch full-port brass valve. You’ll also need two 1-inch adapters going from male NPT (National Pipe Thread) to socket (or “slip”), and one adapter from 1 inch male NPT to a barbed end, sized to match your washer’s outflow pipe. It’s wise to reinforce this joint with a metal pipe clamp as seen in the header image on this page. You can mount all this to the wall above your washer for easy access.
For sink, shower and bathtub drains, you’ll need a larger valve to match the larger drain pipes, commonly either 1-1/2 or 2 inches. They often have to be installed where it’s hard to get to them, such as inside the cabinetry or in the crawlspace under the house. In that case, you can attach an electric actuator to the valve and wire it to a switch inside the house where it’s easy to reach.
Many jurisdictions don’t require permits for L2L systems, provided they follow standard best practices, because they don’t alter the plumbing of the house. You do install some new pipes, but you don’t change the existing ones.
A sink or bathing diversion, on the other hand, requires a permit because you will be altering the existing plumbing.
See our Legal page for more.
If you install an air gap device (also called an air lock vent or in-line vent) in the pipe leading out from your clothes washer to the landscape, the water moving out will pull air along behind it as it goes. You want that.
If you don’t install an air gap, the water will pull more water behind it, potentially including the next volume of new wash water in the cycle. You don’t want that.
If you install it indoors, before the pipe exits the exterior wall, know that if the outflow pipe ever gets blocked completely, the backed up water will overflow through the air gap.
In any case, it should be above the highest point in the outflow line.
Always paint outdoor PVC pipes that are exposed to sunlight to protect them from breaking down over time into carcinogenic compounds.
Always deliver graywater into the landscape below the surface. Never let it flow or collect where animals or people can come into contact with it. Dig a pit or a trench, put in a splash chamber, and fill the pit with wood chips. Microorganisms in the damp chips will break down the impurities in the water, provided you don’t kill them with damaging detergents. See our Soaps page for more.
The beauty of this approach is you don’t need a filter. That’s because the mulch basin is the filter. It’s a bio-filter. The only cleaning you’ll ever do is refill it with wood chips once a year or two depending on how fast they break down. No disgusting goopy hairy filters to clean!
A splash chamber can be as simple as an inverted plastic bucket with a hole cut in the side for your pipe to come through, or you can use irrigation valve box covers. If you use reclaimed materials, make sure to cut a hole in the top (that is, the former bottom) and cover with a lid so you can inspect your outflow from time to time.
Purple is plumbing code for reclaimed water.
For effective gravity flow, slope the pipes at least 2%, or 1/4 inch of drop for each foot of run (in degrees, it’s just under 1.2º).
Laundry machines have a built-in pump that can push water up to a foot above the height of the machine, and horizontally as much as 50 feet away. A 2% slope in that case is not strictly necessary.
Some more elaborate graywater systems will have a surge tank and a sump pump, but you should never store any graywater for more than 24 hours. You wouldn’t want to anyway. It quickly becomes rank.
All-in-one high-tech systems cost thousands of dollars and call for professional installation. The IrriGray system by WaterRenu filters and pumps graywater into graywater-specific drip tubing through standard irrigation valves operated by a standard electronic irrigation controller. Although it has a self-cleaning filter, it still requires occasional maintenance and cleaning.
The AquaLoop graywater system actually cleans graywater to the NSF 350 C standard, which means it can be stored for longer than 24 hours, go out through ordinary off-the-shelf drip tubing, and even be used back in the house for toilet flushing and repeat laundry washing. It works by aerating the water and hosting microbiology that consumes impurities in the water just like the microbes in mulch basins do.
Even with the expensive complicated systems, the same basic principles apply:
For technical specifics in depth, including detailed diagrams and instructions, see the Oasis Design book Create an Oasis with Greywater by Art Ludwig, a pioneer in graywater management and ecological design.
Another easy-to-use guide rich with detail is Greywater, Green Landscape by Laura Allen of Greywater Action.
This is an unusual case study in which graywater-specific plumbing was installed at the time the building was constructed, making a retrofit unnecessary. (See our article about jumping on the opportunity to retrofit during a
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