Rainwater Harvesting for Drylands and Beyond by Brad Lancaster

Soap & Detergent Info

Harvesting greywater is a great way to utilize an on-site non-potable source of supplemental irrigation water, which, along with rainwater, can greatly reduce or eliminate our “need” to irrigate our landscapes with costly potable drinking water, which is the kind of water coming out of most outdoor faucets in the United States. However some of the ingredients, such as salts, that are found in various soaps and detergents can be detrimental to your soils and plants, especially in areas with alkaline soils. Therefore it’s important to select detergents and other cleaning products that have fewer to no ingredients harmful to plants, and to select appropriate vegetation for the areas of your landscape harvesting greywater.

Brief history of soap

(return to top)

Laundry can be done solely with water (no soaps or detergents), but the use of soap became popular due to its ability to lift grease and dirt from clothes. Early soapmakers made their products with wood or plant ashes combined with animal fat or vegetable oil. Many contemporary homemade soaps are made from lye (potassium or sodium hydroxide) from the store and tallow or vegetable oils. Parts of plants such as the soaptree yucca (Yucca elata) and the soap nut tree (Sapindus mukorossi) have also long provided natural soaps.

Synthetic detergents were first developed in Germany during World War I when natural fats and oils were in short supply. The development of detergents was also driven by the search for cleansers that didn’t possess the limitations of traditional soaps or that had additional cleansing capabilities. Synthetic detergents became popular because they did not form a precipitate or soap film; traditional soaps react with the minerals (calcium and magnesium) in hard water to form a precipitate causing “bathtub ring” and the yellowing of clothes. Water softeners were developed to address this issue by replacing calcium in the water with sodium. (Note that rainwater is naturally soft, reducing detergent and soap requirements, and eliminating the need for a water softener, while being a natural hair conditioner.) All kinds of other ingredients, many from petrochemical sources, were also added to detergents to enhance pourability, etc. “Optical brighteners” were developed as a substitute for the earlier blue dyes “blueing” clothes — these brighteners re-radiate a blue light (from absorbed ultraviolet) to cover up any yellow, making your clothes appear “whiter, brighter.”[1] All too often such “new and improved-ments” have made clothes “cleaner,” while making the environment dirtier. (For more info on how and why synthetic detergents are less sensitive to hard water, see www.chemistry.co.nz/introduction.htm and www.britannica.com/eb/article-82263).

Choosing greywater-compatible soaps & detergents

(return to top)

Cleaning products labeled “biodegradable” or “natural” or even “eco-friendly” may not be garden-friendly or “biocompatible,” that is, suitable for the plants and soils of your greywater-irrigated landscape.

According to State of California Department of Water Resource’s Graywater Guide: Using Graywater in Your Landscape [2], specific ingredients to avoid include:

-chlorine or bleach
-sodium perborate
-sodium trypochlorite
-petroleum distillate
-“enzymatic” components

Two common ingredients in synthetic detergents and soaps (including homemade kinds) are sodium and boron. High levels of sodium and other salts in soil are a special concern in arid areas where soils tend to be high in salts already. Salts can raise the alkalinity of soil, degrade the structure of soil, and harm plants. To prevent a buildup of salts in garden soil, minimize your use of soaps and detergents that are made with sodium compounds. Avoid powdered soaps and detergents especially, because in addition to normal amounts of sodium used, they include “filler” ingredients that usually are high in sodium. Instead, use liquid soaps and detergents, which typically use water as their primary “filler” ingredient. The Composting Toilet System Book by David Del Porto and Carol Steinfeld recommends using potassium-based soaps and detergents. Potassium is a plant nutrient and doesn’t cause the problems that sodium-based products do.[3] Traditional liquid soaps (e.g., Dr. Bronner’s or handcrafted soaps) are made from potassium-based lye whereas traditional hard soaps are made from sodium-based lye. Therefore, traditional liquids soaps will not have sodium unless it’s included as an additive. Most liquid soaps and detergents common on store shelves today, however, are made from synthetic compounds, and although these will have less sodium than powdered products, they probably contain some sodium.

Boron, although needed by plants, can be very toxic. It is needed by plants only in extremely small amounts, so avoid cleansers made with boron — including borax.

Avoid chlorine-based products such as chlorine bleach. Instead, use oxygenated bleaches such as hydrogen peroxide. Do not overuse disinfectants since they kill beneficial microbes in the soil.

According to the Graywater Guide, most hand and dish soaps and shampoos will not damage plants if concentrations are low.[4]

Phosphate detergents could be beneficial to plants because phosphorus is an essential plant nutrient, but these detergents also have sodium in them (such as sodium tripolyphosphate).[5] Phosphates in detergents have been banned in many states due to concerns about water pollution (an increase of phosphorus in lakes and rivers causes algal growth). Some detergents may be labeled “environmentally-friendly” because they lack phosphates and thus won’t cause algal growth, however because they are friendly to rivers and lakes does not mean they are necessarily human- or garden-friendly. Low-phosphate detergents can be 100 to 1,000 times more caustic than phosphate detergents so must be used with extreme caution.[6]

A few soaps are being made for use with greywater systems. Art Ludwig of Oasis Designs suggested trying Bio-Pac (check here for smaller containers of Bio-Pac soaps), and Oasis products; for stains, try peroxide bleach.[7]

I prefer to use Oasis brand laundry detergent and dishwashing soap. Both are concentrated liquid soaps. I use the Oasis brand dishwashing soap as a hand and body soap, as well, after I have diluted it to 1 part soap to 8 parts water. For shampoo, I have been using Aubrey Organics brand shampoos after scanning the labels to be sure there are no sodium products in the ingredients.

Handcrafted liquid soaps made from potassium-based ingredients may also be greywater compatible. You can contact soapmakers and ask about their ingredients.

The unfortunate lack of detergent labeling

(return to top)

In the U.S., most soap and detergent manufacturers don’t list their ingredients except in very general terms: “cleansing agents,” “surfactants,” “brighteners,” “enzymes,” “perfumes” etc. — everything beyond that is a “trade secret.” A 1992 study, Greywater and Your Detergent, conducted by the Pima County Cooperative Extension Service and the University of Arizona Office of Arid Lands Studies (sponsored by Tucson Department of Water) analyzed common clothes washing products for ingredients considered potentially harmful to plants.[8] Although this information is not valid for today’s products since formulas change all the time and new products have been introduced, it is an interesting and valuable study. To see the study’s findings click here. Apparently the Water and Environment Research Foundation (www.werf.org) is conducting a new study that should be complete by 2008. Hopefully, in the very near future, legislation will be passed to list actual ingredients on detergent labels (same as with food). The Organic Consumers Association is one organization helping us get there (at least with body care products).

Information on some soap and detergent ingredients is available from the Household Products Database of the National Institutes of Health/National Library of Medicine. Ingredients such as some sodium compounds are listed for common soaps and detergents.

For a general explanation of the characteristics of various detergent ingredients, see

www.epa.gov/dfe/pubs/laundry/techfact/keychar.htm, and

How to get cleaner clothes & greywater with less soap

(return to top)

-Pre-soak your clothes.

-Invest in a more efficient horizontal-axis washing machine. Some have a long pre-soak option, which enhances the cleaning. These machines greatly reduce water, energy, and detergent consumption over conventional clothes washers. (Some use as little as one ounce, or 2 tablespoons, of liquid per load.) They tumble the clothes back and forth and this really helps to get dirt out.

-Use soft rainwater in your washing machine rather than harder municipal or well water. Soft water enhances the cleaning ability of soaps, so you’ll need less.

-Apply your greywater-friendly detergent directly to stains and rub them in prior to washing.

-Apply a citrus-based cleanser such as Citra-Solv to stains.[9]

-Dry your clothes on a clothes line rather than in a mechanical dryer, so the sun can further sterilize your clothes and sun bleach stains.

-Last but not least: Wear clothes with patterns and colors (especially darker colors) that don’t show stains as much! (It’s a not-so-obvious solution that works.)

Ingredient information for some other countries

(return to top)

Click on the link to “laundry products research” from the website below. There you will find great information on the various ingredients of different products, and what those products mean for your plants and soil.

Good information on what ingredients do, and recent analysis of ingredients of brands sold in India.

Note: the Navdanya Biodiversity Conservation Farm in Ramgarh, Dehra Dun, Uttaranchal, India, has been experimenting with using the soap nut from the soap nut tree (Sapindus mukorossi) as a biocompatible soap in their communal kitchen and laundry, the greywater from which is then reused in the landscape. From what I observed, all seemed to be working well.

Body-care products tips: more ingredients to avoid

(return to top)

Avoid products containing any form of paraben (methyl, propyl, butyl, and ethyl). According to the Organic Consumers Association, paraben “is a very commonly used synthetic preservative that has been shown to alter hormone levels, possibly increasing risks for certain types of cancer, impaired fertility, or alteration of the development of a fetus or young child.” [10] (See www.organicconsumers.org for more information.)


(return to top)

1. Flatow, Ira. Rainbows, Curve Balls, & Other Wonders of the Natural World Explained (NY: Harper, 1988).

2. Graywater Guide: Using Graywater in Your Landscape (State of California, Department of Water Resources, 1995). www.owue.water.ca.gov

3. Del Porto, David and Carol Steinfeld. The Composting Toilet System Book: A Practical Guide to Choosing, Planning and Maintaining Composting Toilet Systems, an Alternative to Sewer and Septic Systems (Center for Ecological Pollution Prevention, 1999).

4. Graywater Guide.

5. www.chem-online.org/detergent-chemical.htm

6. Purdue University in cooperation with U.S. Environmental Protection Agency. Software for Environmental Awareness (Purdue University, 1997, updated 2005). www.epa.gov/seahome/index.html (search on “Solid/Hazardous Waste” and “Household Waste Management”)

7. Ludwig, Art. Oasis Design website, Greywater FAQs.

8. Pima County Cooperative Extension Service, University of Arizona Office of Arid Lands Studies, Tucson Department of Water. Greywater and Your Detergent (research conducted in 1992). Available at www.harvestingrainwater.com, “Greywater Harvesting” webpage.

9. Del Porto and Steinfeld. The Composting Toilet System Book.

10. Organic Consumers Association, “Organic Body Care Tips,” Organic View (Autumn 2004).

Drops in a Bucket Blog

 »Read all blog posts...

Upcoming Events

Also see the full list of upcoming events.

Umbrella Newsletter

The Umbrella: Spring Equinox 2017

A catch-all of resources,
events, media, and more
from Brad Lancaster
Spring Equinox 2017
Around here we like to rhyme with the seasons whenever possible. In this case, that means welcoming the fast-approaching beginning of SPRING (the Vernal Equinox (in the northern hemisphere) is March 20 this year in Tucson, and marks one of only two […]

 »Read all newsletters...

Like what this website offers?

Donations are greatly appreciated as they enable us to continuously update this expansive resource and generate new content. Thanks!