The first thought that many conversation minded individuals have after taking a shower is often, “how can I reuse all that water?” Using ‘grey water’ like bath water to irrigate your garden may be a good alternative, if you know the right shampoos to use that won’t hurt your plants.
Is it OK to use soapy water to water plants? Yes, but stay away from soaps that contain sodium, borax, chlorine, petroleum distillates, or is not PH neutral. Taking steps to dilute the soap, and spread it out over the garden rather than accumulating the soap all in one spot can help your organic soaps naturally biodegrade and feed your garden.
How To Know If Your Shampoo is Safe for the Garden and Grey Water Systems
In many cases, shampoos are so highly diluted that relatively small amounts mixed in with grey water won’t cause a serious problem for plants. But, if you intend to water consistently with grey water, or install a grey water system, it is best to take steps to ensure potentially harmful substances in some shampoos don’t build up in your plant beds.
Plus, grey water safe soaps should be people safe soaps as well, and may result in a healthier more organic lifestyle.
I recommend you follow following steps to make your grey water safe for the garden:
- Ensure your shampoos are free of potentially toxic compounds such as:
- Boron, borax, chlorine, bleach
- Peroxygen and sodium perborate
- Petroleum distillate or alkylbenzene
- Dilute soap water as much as practical (by using a grey water collection and mixing tank for example)
- Implement a distributed irrigation system or buffer zone for grey water watering
Recommended Grey Water Safe Shampoos
There are so many soaps out there, and their ingredient lists are often so confusing, that it can be hard to find the right grey water safe option for your. Although there may be hundreds of grey water safe shampoo options out there, these three are commonly recommended or my favorite picks for use with a grey water system.
Dr. Bronner’s Pure-Castile Soap
Dr. Bronner’s Pure-Castile Soap is a long time favorite, and hard to beat even still in the world of organic soaps. Don’t be frightened by the all the world on the label, the list of ingredients is amazingly short and easy to see how it would be safe for the garden.
It is a potassium based soap, which is thought to be safer for plants than the more common sodium based soaps. The rest of the ingredients are mostly organic oils, plant scents, citric acid, and (tocopherol)[https://en.wikipedia.org/wiki/Tocopherol] many forms of which are classified as vitamin E.
With relatively low cost compared to other organic soaps, a almost unbeatable clean ingredients list, and wide range of scents (and unscented) to choose from, Dr. Bronner’s is probably the best pick for organic grey water safe shampoos.
Laritelle Organic Shampoo
Larietell Organic Shampoo is a nice, premium level shampoo that ticks many of the safety boxes that I look for use in a grey water system. The organic goodness of the shampoo is backed up by the fact that many people who use it found their hair growing in thicker after using it.
An in depth look at the ingredients only brought up one potentially questionable compound: Sodium Alginate, but which is mostly produced by brown algae, and apparently helps block absorption of radioactive isotopes in the body. So, I’m not too worried about it affecting plants. The majority of the rest of the ingredients are plant extracts which are said to be harvest from pesticide free sources, and which impart the wonderful fragrances of this Earth friendly shampoo.
Aubrey Organics Shampoo / Conditioner
Aubrey Organics Shampoo comes in on the more affordable side of the spectrum of the shampoo world, and highly recommended by other sources for grey water safe shampoos. Although I haven’t used it myself, a quick look through the ingredients seems to indicate it would be safe for grey water use.
To my eye, the most questionable ingredients are the sodium cocyl related compounds, such as the main soap (surfractant) compound sodium cocyl isethionate, because they are sodium based soap formulations. However, there is some research that sodium cocyl isethionate is relatively mild on the human skin barrier, and thus is likely to be relatively safe for use in the garden as well.
I wanted to cover this product because I see it recommended so much, but honestly I feel like more data is needed to tell if it is 100% garden safe or not. If in doubt, you can’t go wrong with my first two recommendations.
Avoiding Toxic Ingredients in Your Grey Water Shampoos
The recommendations I follow regarding grey water safe shampoos come from the State of California Water Department (PDF). They provide a long list of potentially harmful compounds to watch out for on your shampoo labels. Be careful, and take the time to read the long list.
Many “organic” or otherwise well marketing and nice looking shampoo options contain potentially harmful substances that could do damage to your garden. Even if the label looks good, don’t be taken in by a fancy facade. Take the time to do your research, or try on of the soaps that I use above.
One lower cost option, if you cannot afford organic grey water safe shampoos recommended above is to make your own shampoo at home. The process for shampoo is relatively simple, because you are not trying to make a thick bar. And, plant safe potassium hydroxide based soaps are naturally liquid.
DIY shampoos can be made with your potassium hydroxide source (food grade available cheaply online), base oil of choice, essential oils for scent, and your choice of oils and all natural bonus ingredients. The key to making plant healthy shampoos is to make sure the mix comes out neutral, which can be accomplished carefully following an known good recipe. Or, even better, measure the outcome with a low cost PH test meter. No more annoying little strips necessary to get the highest quality PH balanced organic shampoo, just stick in the end and read the number!
Does Grey Water Kill Plants?
Whether grey water will harm your plants depends entirely on what substances you put in your grey water. Organic soaps and shampoos that stay away from ingredients toxic to plants such as sodium, borax, boron, and petroleum distillates are frequently safe for use on plants. Especially if sufficiently diluted, distributed, or filtered through buffer zone plants.
Is Borax safe for greywater?
The State of California Water Department (PDF). Does not recommend borax for use in grey water systems. Borax in large concentrations is recommended for use as a diy weed killer, although it is said that in small quantities (6-7 tablespoons / 1000 sqft) it can be an effective fertilizer. Avoid borax if you can, but you will probably be safe if you only use it infrequently, in small quantities, and spread borax contaminated grey water over a larger area of the garden.
Will GREY water kill grass?
If you take steps to ensure your grey water is free of toxic substances, then it can be safe for use on lawns and grass. Many shampoos, soaps, and other cleaners contain sodium, boron, borax, petroleum products, bleach, or other that could affect your grass over time. Take a look at my recommendations above for grey water safe shampoos and soaps, and in the article Safe Detergents and Soaps for Grey Water Systems to learn more about how to choose safe substances for use with your grey water system and for watering your lawn with grey water.
Can I water my garden with greywater?
Yes. Grey water is free of potentially harmful chemicals is safe for use in the garden, in that it won’t kill your plants. If you intend to water vegetable gardens, be sure to take proper steps to mitigate potential health hazards. If possible, only use grey water on trees or ornamental plants.
