For off grid and permaculturists, reusing mildly dirty water in a “grey water” systems is a no brainer since it saves money, conserves water, and finds a use for every waste. But, for the beginner it can be a little scary, because you don’t want to accidentally poison your plants in the process. Don’t worry, using grey water safely can be very simple, and I’ll walk you through what you need to know.
What soaps are safe to use in a grey water system? Anything except:
- Don’t use bleaches
- Don’t use products labeled as whitening, softening, or containing enzymatic powders
- Don’t use any product with these ingredients:
- Boron, borax, chlorine, or bleach
- Peroxygen or sodium perborate
- Petroleum distillate or alkylbenzene
This information comes from the State of California Water Department (pdf), and is enough to get you started. But for more detailed information on exactly what you need to watch out for, recommended soaps for grey water systems, and other ways to filter your grey water, read on.
What Can’t I Put Down My Grey Water System
I general you need want to avoid cleaning products with contaminants that can kill your plants and turn the discharge area in to a barren waste land. First off, any poison or something you would need gloves to use is probably off limits for a grey water system. Even still, watch out for the following issues:
Avoid Salt (Sodium) in Grey Water
Sodium salts — commonly found in table salts and other sodium substances in soaps — are a poison that will kill plants in high concentration. Avoid cleaners which contain salt, and divert any salty kitchen waste away from your grey water system.
Keep Grey Water PH Neutral
Overly acidic or basic (aka alkaline) water will affect the soil stunting the growth of some plants.
Some soaps and detergents advertise themselves as PH neutral, but others may be and don’t say. One sure way to tell to to buy an inexpensive digital PH meter. To test wash something as you normally would and test the waste water by touching it with the end of the meter. The amount of water you use affects the PH, but shoot for anything between 5.5 and 7.0.
If you don’t want to spring for a meter, then a good rule of thumb is that many liquid soaps are PH neutral, but bar / solid soaps tend to be acidic.
One option, if you do have an acidic soap is to plant acid loving plants like:
- or Blueberries
near the outlet of your waste water system.
Do Not Use Chlorine Bleach
Chlorine bleach is very toxic and should not be used in grey water systems. If you need something with whitening power to use with a grey water system, consider replacing bleach with hydrogen peroxide, which breaks down to water and oxygen naturally, and is non-toxic in commonly sold concentrations (3%). Be careful with hair bleach or “food grade” peroxide, which can cause burns in not handled properly.
What Soaps and Detergents are Recommended for Grey Water Systems
Based on a list from Grey Water Action, here are a few recommendations for grey water safe soaps and detergents.
Grey Water Safe Laundry Detergents
Grey Water Safe Soaps
Grey Water Safe Shampoo, Conditioner, and Shower Products
- Aubrey Organics Shampoo
- Aubrey organics Conditioner
- Alaffia Face Cleanser
- Dr. Bronners’s Pure-Castile Soap
Grey Water Safe Dish Soap
How to Make Grey Water Safe Soap and Laundry Detergent
If you are worried about the expense or difficulty of finding a completely natural grey water safe soap or detergent, consider making your own with natural ingredients and fragrances. It is not very difficult, and produces a superior quality product.
Making Grey Water Safe Soap
Making grey water safe soap is easy. Just find any old-fashioned soap recipe such as this one which doesn’t use lye, aka sodium hydroxide. Lye contains sodium which will stay in the soap after you are done making even though the lye will not.
Be sure to test the PH of your soap after you make it, because adding more KOH (potassium hydroxide) or other base to soap than necessary can leave it overall basic, which could harm your plants. Measure your ingredients carefully, or err on the side of less KOH, which produces a slightly more moisturizing soap.
Making Grey Water Safe Detergent
Most DIY homemade detergent recipes have you start with the soap of your choice, and mix in washing soda, baking soda, and borax (or some combination of the three). However, besides the soap, none of these products are recommended for a grey water system.
- Borax is not suitable for use on plants.
- Washing soda contains sodium
- Baking soda is overall basic
My first recommendation is to replace your laundry detergent directly with a liquid soap such as Dr. Bronner’s, or one you make yourself as above.
If you feel your laundry needs a little clean boost, you can add a few cups of baking soda in to a load of laundry. Check the PH to see if it is too basic, but you might get away with this depending on how much other water you send through your grey water system. Or, you could add an equivalent amount of a natural acid such as vinegar or lemon juice to the wash near the end, to neutralize the water back down to a PH of 7.
Are Bio-Degradable Soaps Safe for Grey Water Systems?
A product being labeled as biodegradable does not necessary mean that it is safe for a grey water system. Anything that breaks down naturally in the environment can be considered biodegradable, and most grey water safe products should be biodegradable, even if they aren’t labeled as such. But, just because a product is biodegradable, doesn’t mean the product won’t kill your plants. Be sure your soaps are chlorine free, sodium free, borax free, non-toxic, and PH neutral to ensure they will not damage your grey water system.
Which Plants Can Be Used to Filter Grey Water?
Some sources suggest filtering water through special plants to help clean the water. In general, passing the water through a layer of mulch or top soil is enough filtering if you follow the recommendations above.
If your grey water is too acidic, you may have better luck if you plant acid loving plants near by: such as fern, rhododendrons, or blueberries.
If your grey water is too salty, you can possibly get by creating a constructed wetland where your grey water exits the system. I recommend researching and using local wetland species specific to your region. Only go this route if you use your grey water system enough to keep the ground soggy most of the year, or you already have a small wetland area on your property which you can use for this purpose.
Is Borax Grey Water Safe?
No, borax is not considered safe for plants and should not be used in a grey water system. source
Can You Use Grey Water to Water Plants?
Yes. If you are careful to use grey water safe soaps and cleaners (see above) then you can water plants with grey water. Don’t let grey water touch edible parts of plants or human skin. Grey water irrigation is best done through underground drip lines.
Is Dish Soap Bad for Soil?
Some are and some aren’t. If your dish soap contains sodium, borax, chlorine, petroleum distillates, or is not PH neutral, then do not let it get in to the soil.