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FROM THE ARCHIVES: Greywater - Re-using “Waste” Water Can Reduce Irrigation Water Needs

By Will Johnson.

Originally published in Let’s Talk Plants! October 2008, No. 169, and not updated.

Photo credit: Wikimedia Commons general license w/permission from The Sustainable Sanitation Alliance (SuSanA) which is a network formed by organizations active in the field of sustainable sanitation.
June 2008, Urban decentralized greywater treatment garden in Oslo, Norway.

Greywater is defined as “any wastewater generated in the home, except water from toilets.” Laundry, shower, sink, and dish water comprise up to 80% of residential “wastewater”; toilets use most of the rest. Greywater is particularly suitable for re-use irrigating shrubs and trees in the landscape. Keep in mind that the re-use of greywater in California is regulated by very strict/prohibitive building codes. A few states, notably Arizona, have very reasonable greywater regulations; the systems described here are generally in accordance with Arizona guidelines. Hopefully, California will soon follow Arizona in adopting reasonable, safe guidelines. Until then, while what we’re describing may indeed be safe and environmentally correct, it may violate certain building or health and safety codes.

Disclaimer: Neither the author nor San Diego Horticultural Society encourage you to violate any laws! Having said that, let's start re-using some valuable water!

Greywater can be further divided into “clearwater” (warm-up water from the faucet, A/C condensation, and R/O purifier drain water), which is great to reuse, and “dark greywater” (laundry water used to clean diapers, or solids-laden kitchen sink water), which isn’t suitable for irrigation.

Toilet-flush water is called “black-water” due to the presence of harmful and potentially dangerous bacteria in large numbers, and though a few systems can safely recycle this, our discussion here will skip this.

The simplest two sources for irrigation re-use are your shower and your laundry. An average shower may generate up to 30-50 gallons of water and a large load of laundry from a typical top-load washing machine will use 30-40 gallons per cycle. If your house is constructed allowing easy access to the drains for showers and laundry (such as a raised foundation), you may want to seriously study the re-use of greywater for your own home. One excellent resource for further research is The Greywater Guerrillas (, who recently conducted a demonstration greywater branched-drain installation here in San Diego. The undisputed expert in the field, is Art Ludwig. I own a couple of his books, and recommend you visit his site ( if you want to do-it-yourself.

Diverting greywater almost always involves a diverter-valve, also called a Jandy valve, to switch the path of water either to the sewer, or to the landscape. By locating this valve in a convenient location, you can make sure that only the desirable greywater goes out to your yard. With all greywater systems the water flows directly to the ground below a level of mulch, never sprayed into the air.

We’ll look at just three of the simplest versions of greywater systems. First, an outdoor shower that drains to the landscape is called Landscape Direct. Many urban residences may be unsuitable for this, but I can personally attest to the pleasant experience showering out in nature can be. By plumbing hot and cold water to an outdoor shower, the shower drains directly through a branching drain-pipe system to nearby mulch basins. These drain tubes can be moved from one basin to another nearby basin to control moisture levels.

The types of soaps, shampoo, or detergents being used are very important, for example, Boron, from laundry detergent is often toxic to plants. Many types of soaps, conditioners, and most laundry detergents may be labeled “biodegradable” (they break down), but are not “biocompatible” (breaking down into useful, or at least, not harmful components), so choose the right soap/detergent! The hands-down favorite brand of laundry and dish soaps are Oasis, available from, and for the shower & bath: Dr. Bronner’s. An interesting organic and reportedly effective product are “soap nuts,” the fruit of the Sapindus mukorossi tree. I’ll be buying some of these to try out at home. Interestingly, products by Seventh Generation, an organic, biodegradable “socially conscious” company, are not rated as biocompatible due to higher than desirable residual mineral levels.

Second, one great beginner system involves diverting waste water from your top-load washing machine. Because the washing machine has a powerful pump, it can assist in moving water out away from the house into an elevated surge basin, so you can irrigate farther from the greywater source. Again, a diverter/Jandy valve allows for switching between sewer and landscape, in the event you happen to wash a load of clothes soiled with disease or human waste. When the washer drains, the waste water is pumped out thru the Jandy valve via inexpensive PVC or poly tubing to an elevated barrel, called a surge basin. From the surge basin, one-inch distribution tubing (usually PE - polyethylene tubing) drains the greywater to the mulch basins.

A homeowner can do much or all of the work involved in installing this type of system, though a plumber might be required to install the diverter valve, which is often located inside the building. You do NOT want a problem involving flooding with wastewater inside the house!

The third great “low-hanging-fruit” is a system which uses your shower water. Few people use a shutoff valve (or turn off the water) when soaping up; as a result we waste many gallons of relatively clean water that is useable for the garden. Because the shower drain pipes are at a lower elevation, relative to the garden, reuse is likely more restricted. Without a pump, greywater only flows downhill, needing a 1/4′′ drop for every foot of run. The gravity limitations require some thought, as many sites are challenging or unsuitable due to a lack of fall. At my own home, I have plans to reuse shower water to irrigate a lovely mature Corkscrew Willow when I remove the front lawn in the next month or two. With the lawn removed, the tree will lose its primary source of water, and will begin to look terrible. As a riverbed native, a willow needs ridiculous amounts of water (compared with native trees), and I’m not inclined to use my tap water to keep it healthy. Fortunately, the tree is within reach of the gravity-fed shower system, and with four adults using the shower, it will be very happy! To be a good neighbor, I even checked the idea with my adjoining neighbor, and he agreed it’s a great idea.

With a dry fall, we are likely to have mandatory water reductions, and personally, I believe it will only get worse. By using all available methods to make the best use, and re-use of the water we consume, we become part of the solution to the problem.


In October of 2008 SDHS member Will Johnson, was a C27 landscape contractor, who lived with his family in Kensington. His company, SECO Landscapes, was a SDHS sponsor, specializing in complete outdoor living/landscape installation, water gardens, night lighting and irrigation management.


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