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Greywater, Green Landscape

Posted by Green Builder Staff

Apr 4, 2017 8:31:00 AM

In Greywater, Green Landscape, author Laura Allen teaches readers how to plan for and install their own system, starting by identifying greywater sources in the home and estimating flow rate. She then helps readers pinpoint which areas or specific plants will reap the greatest benefit from redirected wastewater.

These simple, accessible systems — requiring only basic tools and materials readily available at home supply stores — are well within reach for the average DIY homeowner and gardener. With only a little work, homeowners can make a big difference.

Detailed instructions and step-by-step photographs guide readers through installing a variety of systems, including laundry-to-landscape and branched drain gravity-fed setups.

In the preview chapter below, you'll learn how to estimate how much greywater your home produces and which greywater sources (called fixtures) you can tap into.

Identify Your Greywater Sources

If you’re hoping to use greywater from your existing home, you’ll find that some grey-water sources are easier to access than others. If you’re building a new home, you have much more flexibility as to which sources you tap into — and where. Diverting greywater from drainpipes often requires installing a diverter valve (called a 3-way valve) that enables you to switch the water flow between the drain line (leading to the sewer or septic system) and the greywater system. Diverter valves can be operated manually or remotely, via an electrical switch. First we’ll look at the primary potential sources for greywater in a home, then we’ll discuss the details of tapping into a home’s drain system.

Laura Allen Greywater Washer

Clothes Washers

Washing machines offer the easiest source of greywater to reuse. The machine’s internal pump pushes greywater out through the machine’s drain hose; from there you can reroute it to the landscape without changing the existing drainpipes. I’ve worked on hundreds of laundry greywater systems, and they’re consistently the easiest and simplest of the greywater options.

In most homes, a greywater pipe begins its route toward the landscape by exiting the laundry room through the wall or floor. Think about how you could send a new pipe from your washing machine out to the landscape. Can it go out through the wall or down into a crawl space and then outside? If your house has a concrete slab foundation and your machine is in a room without exterior walls, the only way to send the water outside is to run the pipe through another room in the house, perhaps hidden under shelving or along a baseboard.

It is easy to live with a laundry greywater system. There are several commonly available greywater-compatible detergents that allow you to safely irrigate plants with the greywater from regular laundry loads. For times when you want to use bleach or wash soiled diapers, just turn the valve located next to the washing machine and redirect the water to the original drain.

Showers and Baths

Showers and baths produce large volumes of good irrigation water, although diverting it to the yard can be tricky, particularly in existing homes. The next section will help you navigate your drainpipes to identify these potential greywater sources. If you are inexperienced with plumbing, this aspect may feel confusing; consider finding a handy friend or plumber to be your reading buddy. Or, read on to develop your greywater sleuthing skills; it can be fun and empowering to uncover the mysteries of the household plumbing system.

Bathroom (Lavatory) Sinks

Since they typically produce such small quantities of greywater, bathroom sinks don’t warrant a big investment for a system, though sometimes it’s easy to reuse the water. In my house the downstairs sink was easy to divert to irrigate a nearby pomegranate bush and male kiwi vine, whereas the upstairs sink would have been more involved so we just detached the drain to bucket-flush the toilet (we were careful to plug the drain line to prevent sewer gases from entering the bathroom).

Easy options include:

  • Combine the sink greywater drain with the shower/bath drain and divert the greywater after both sources have combined.
  • Install a diverter valve under the sink and direct water to one or two nearby plants in a tiny branched drain system.
  • Alternatively, disconnect the sink drain and collect greywater in a bucket to bucket-flush the toilet. Experiment to find out how much water it takes to flush your toilet: empty the bucket directly into the toilet bowl (not the tank), and the toilet will flush.
  • Install a SinkPositive system: a faucet and small sink-bowl that replace the toilet tank lid (see Resources). When you flush the toilet, fill-water flows out the little faucet and through the sink-bowl so you can wash your hands as the toilet tank refills.

There are manufactured greywater systems designed to collect, filter, and disinfect bathroom sink greywater below the sink and then pump it into the toilet tank for flushing. I know a few people who have tried these systems, and each had numerous problems with them. Consider other options first if you plan to reuse sink water.

Kitchen Sinks

Kitchen sinks usually produce a plentiful supply of water that can be diverted from the sink drain inside the house. Kitchen greywater tends to contain food scraps and grease, so it takes more effort to maintain the system than with those for other greywater sources (see Filtering Kitchen Greywater with Mulch Basins on page 16).

Some states consider kitchen water “greywater,” while others consider it “blackwater,” like what comes out of the toilets. If your state doesn’t call kitchen water “grey,” a legal installation will be more challenging. With determination and an open-minded building department, it’s possible to get an experimental permit or use the “alternative materials and methods” section of your state’s code.

Divert kitchen water directly below the sink for easy access to the pipes and diverter valve. The greywater pipe needs a route to the landscape, and you can send it below the floor or directly out of the house, depending on your situation and climate. Local code may require the diverter valve be located downstream of the vent connection.


“Excerpted from Greywater, Green Landscape, © by Laura Allen, photography by © Leigh Jerrard, Greywater Corps., illustration by © James Provost, used with permission from Storey Publishing.”

About the author

Laura Allen is the author of The Water-Wise Home and cofounder of Greywater Action, a collaborative of educators who teach residents and tradespeople about affordable and simple household water systems that dramatically reduce water use and foster sustainable cultures of water. She leads classes and workshops, including the first training program for professional greywater installers, and participates in writing state government greywater and composting toilet codes. She lives in Eugene, Oregon.


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