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Greywater Harvesting

Greywater, sometimes spelled graywater, is lightly used drain water from sinks, showers/bathtubs, and washing machines, but NOT toilet drain water, which is called “blackwater.”

Rain- and greywater-harvesting garden on periphery of small yard in Tucson, AZ.
Roof runoff is directed to basins via a downspout, then pipe (beneath the path—see dotted blue flow arrow). Kitchen-sink dark-greywater is directed to basins via a branched-drain pipe system (purple dotted pipe). Washing-machine greywater is directed to basins via a multi-drain system (purple dotted pipe). With each load of laundry the washing machine’s drain hose is rotated from one greywater drain to the other (each discharging greywater to a different section of a mulched basin and its plantings). Greywater is discharged to multiple points, rather than one, to ensure soil stays aerobic and odor-free. All systems use gravity to distribute the water for free. Thus all pipes maintain a minimum 2% slope (1/4-inch drop per horizontal foot, or 2-cm drop per horizontal meter).
Photo: Brad Lancaster

Greywater harvesting is the practice of directing greywater to the primary root/life zone (top 1 to 2 feet, or 0.3 to 0.6m, of the soil) to freely irrigate and help grow beautiful and productive landscapes while achieving “waste” water treatment without using chemicals or energy. Plants and microorganisms in the soil consume and filter the organic nutrients and bacteria found in greywater, treating it naturally and returning clean water to the water cycle. The number and diversity of these beneficial microorganisms and plant roots increase the closer you get to the surface of the soil, so typically—the higher you distribute the greywater in, or atop, the uppermost layers of the soil—the better.

The practices I advocate have no stinky tanks, costly mechanical pumps, nor their maintenance headaches. Instead, the systems I advocate use gravity and living pumps of perennial vegetation and other life to freely distribute that greywater.

Greywater harvesting turns a free, on-site “waste” water into a safe and productive resource water available for irrigation in times of no rain as long as you are home using water. And there is typically a significant amount of greywater available.

The above graphic, courtesy of Tucson Water, shows how an average household in Tucson, Arizona uses its potable water delivered via the city’s water line. Note how the largest use (outdoor – 45%) is primarily for irrigation. Then note how the water used in washing machine, faucets, and shower (combined 32%) could meet most of the outdoor water needs IF the greywater from the laundry, sink, and shower drains were directed to the landscape, instead of the sewer or septic

What about my water needs not met by greywater, or when I’m not home?

The remaining outdoor water needs—not met by harvested greywater—can typically be met with the harvest of other free on-site waters such as rainwater, stormwater, dark greywater, snow, and/or AC condensate or dew.

Additional benefits of harvesting greywater as I advocate

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See the new, full-color, revised editions of Brad’s award-winning books
– available a deep discount, direct from Brad:

Book Cover #2

Volume 2

For more information on various gravity-fed greywater-harvesting systems; and how to place, design, size, implement, and plant them in balance with your soil’s percolation rate for maximum positive effect:

• Read the greywater chapter and appendix 3 in Rainwater Harvesting for Drylands and Beyond, Volume 2 —available at deep discount direct from the author.

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