Greywater systems are a wonderful way to save water, however, the products that we use to clean ourselves and our homes with may have an effect on the soil and plants that are watered with it. I am often asked the question if my soap is good for greywater systems; so, here are some things to know.
First, let’s define greywater.
Greywater is the term used to describe water segregated from a domestic wastewater collection system and reused on site. This water can come from a variety of sources such as showers, bathtubs, washing machines, and bathroom sinks. It contains some soap and detergent but is clean enough for non-potable uses. Water from toilets or wash water from diapers is not considered to be greywater. Kitchen sink water is not considered greywater in many states. Many buildings or individual dwellings have systems that capture, treat and distribute greywater for irrigation or other non-potable uses. [See 1]
Why be cautious about which soaps and cleaners are used with a greywater system? Studies show that long-term irrigation with greywater may result in accumulation of salts, surfactants and boron in the soil. [See 2] Many products are labeled “biodegradable”, “natural” and “ecofriendly”, but if they contain salts and boron, they can be harmful to plants and the soil. Another consideration is that some soaps may change the pH of soil to alkaline; acid loving plants may not like this type of water. These include plants like ferns, rhododendrons, and blueberries. [See 3]
Another source indicates that the amount of sodium in shower greywater is negligible and has no impact on plants and that the effect on pH overall is negligible due to dilution and as long as the water is well dispersed evenly across the garden and not concentrated in one area. [See 4]
Which Mountain Girl Soaps can I use with my greywater system?
All Mountain Girl soaps are biodegradable and non-toxic. The pH is approximately 8. None of them contain boron (borax).
Safe to Use: Mountain Girl’s liquid soap and foaming facial cleanser is made with potassium, rather than sodium, hydroxide and therefore does not contain salt. It is safe to use in a greywater system. The soap will be very diluted and should not have an effect on the pH of acid loving plants.
You Decide: My bar soap is made with sodium hydroxide and contains salt. The effects of sodium and pH should be insignificant. You can further minimize any impact by evenly irrigating across the landscape.
Where can I find more information?
There are a lot of other considerations for greywater systems, such as the use of water softeners, chlorine bleach, etc. Here are some resources where you can find more information.
Beginner Guide to Greywater Systems
Greywater Compatible Soap & Detergent Info
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