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The best greywater-safe laundry detergents are Oasis and Bio-Pac, both salt-free, biocompatible liquids made for laundry-to-landscape systems. Dr. Bronner’s castile soap is a close second.
Below: why “biocompatible” beats “biodegradable,” and which ingredients to avoid.
Biodegradable soaps can break down in the environment, but if they’re made of harmful substances, they can still break down into harmful smaller parts. Merely biodegradable is not good enough.
Biocompatible means a compound that breaks down into parts that are compatible with life. You want soaps that are going to feed your plants. That’s truly graywater-friendly.
Our top recommended graywater-safe laundry detergent is Oasis Biocompatible, the gold standard in graywater laundry. It was developed for the express purpose of using in laundry-to-landscape systems. And it’s concentrated enough to use only 1 ounce per load in modern HE (high-efficiency) washers, making it highly economical.
They also make a biocompatible dish soap/all-purpose cleaner.
Not everything is made to biocompatible standards yet. So there is a second rule that’s much easier to follow:
Leave out the sodium.
Sodium is salt, and salt buildup in your soil over time will ruin its ability to sustain life. This has been a problem for almost every irrigation-based civilization in the world throughout history. There’s no need to help the process along with your eco-friendly water systems.
It’s especially true for dry climates such as most of North America west of the 100th meridian – which goes through eastern Mexico, Texas, Oklahoma, Kansas, Nebraska, North and South Dakota, and up into Manitoba.
The point to remember is, if you have more evaporation than precipitation in a year, there’s not enough rainwater to flush out the salts being deposited.
This is what you don’t want to see:
Eco-friendly soaps for sustainable living use potassium-based ingredients.
Examples to look for:
You should also leave out boron, borax and borate. The best rule of thumb here is to never use anything powdered. For one thing, powders normally use sodium-based ingredients as fillers. Liquids use water as filler.
Bleach is a biocide. Choose hydrogen peroxide instead, because it breaks down to water and oxygen. You could also use vinegar, lemon juice, or liquid Castile soap, all of which promote environmental sustainability.
Plants depend on healthy soil biology. See Dr. Elaine Ingham on the Soil Food Web.
Although it goes without saying, we’ll say it anyway: Never use antibacterial soap if you’re sending to the microbes. This counts not only for laundry but also your hand-washing sinks that you want to send out to your soil food web.
“Bleaches, disinfectants and germicides, even if from ‘natural’ products, will impact soil health by killing living organisms.”
If you just have to use something that’s dangerous or poisonous to soil biology (standard mouthwash, for example), that’s why your graywater system is built with a clearly labeled and easily accessible 3-way diverter valve, so you can direct the junk into the sewer for as long as it’s flowing down your pipes. See our Build page for more.
Developed by graywater pioneer Art Ludwig and later sold to Bio-Pac, Inc., Oasis biocompatible laundry detergent breaks down completely into plant nutrients with nothing left over to damage soil biology.
Bio-Pac’s own liquid laundry detergent has almost the identical recipe, just with a different amount of Limonene, a citrus extract.
Both Oasis and Bio-Pac are hands-down the best laundry detergents for graywater reuse.
Don’t use Bio-Pac dry powder for your graywater, however. It’s full of sodium ingredients.
Dr. Bronner’s castile soap is potassium based and is the second most recommended laundry detergent for graywater reuse.
You can also use it as a shampoo if you follow it with their hair conditioning rinse.
Have a look at their guide to using Dr. Bronner’s as shampoo, as well as Lisa Bronner’s original post on hair washing. You might be surprised.
Did you know they also have a leave-in conditioner hair créme? It’s also suitable for graywater!
Even in hard water, Dr. Bronner’s can leave your hair feeling soft and clean, and feed your living landscape.
And if you’re one who thinks Dr. Bronner’s doesn’t lather up like other soaps, recall what we learned during the Covid shutdown: If you scrub your hands together for the duration of Twinkle Little Star or The Alphabet Song, you know Dr. Bronner’s kicks up a perfectly great lather! You just have to do it away from the stream of water that’s simultaneously washing it all away.
Interestingly, while solid soaps normally rely on sodium ingredients for their solidity, and some sodium usually remains after manufacturing, the label on Dr. Bronner’s Castile bar soap states that the single sodium-based ingredient, sodium hydroxide, does not remain in the soap after the saponifying process, which would make it an eco-friendly soap brand for sustainable living even in a solid bar.
The third most recommended laundry detergent for graywater use is Soap nuts, also known as soap berries. They are the dried fruits of Sapindus mukorossi or Asian soapberry tree, and are naturally high in saponin, a natural cleansing compound. A few soap nuts in a small cloth bag added to the wash can be used many times over before losing the ability to produce suds.
Read what LisaLise has to say about using soap nuts to clean her laundry for a year.
There are a lot of attractive options that call themselves “green” and “ecological.” They are better than standard industrial products, until it comes to graywater. Read our article about why options like Ecos and Ecover aren’t enough.
One of the main reasons people use standard laundry detergents with harsh and soil-damaging ingredients is that they have hard water, which interferes with the cleaning process. A water softener helps, but the trouble is, water softeners also put salt into your soil (an alternative is to use potassium chloride in your water softener instead of sodium chloride).
But here’s something you can do that’s next-level: rain water has no minerals in it, meaning it’s naturally soft. So if you capture rainwater and run it back into your house to use in the laundry, you’ll bypass the need to use all those dastardly soil-killers!
Best to check with your local authorities about the need for permits if you change the existing plumbing, like tapping into the potable water supply heading into your washer. See our Legal page for guidance.
Liquid dish soap for washing dishes by hand is one thing; detergent for your automatic dishwasher is another story altogether.
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