Why Detergent Choice Matters for Greywater
The detergent you use in your washing machine goes directly into your landscape when you use a greywater system. Most conventional detergents contain ingredients that, over time, can degrade soil structure, accumulate to toxic levels for plants, or harm the microbial life that makes soil productive. Switching to a greywater-compatible detergent is one of the most important steps in running a healthy long-term system.
The good news: greywater-safe detergents are widely available, often cost the same as conventional options, and typically perform comparably on everyday laundry.
Ingredients to Avoid
Sodium (Salt)
This is the #1 concern. High-sodium detergents cause soil "dispersion" — clay particles separate and the soil loses its structure, becoming compacted and impermeable over time. This is called sodium toxicity in soils, and it's a real problem in greywater basins that receive years of high-sodium water. Look for detergents that use potassium (not sodium) as their base, or specifically marketed as "low-sodium" or "sodium-free."
Sodium content isn't always labeled directly. Check for these sodium-containing ingredients: sodium lauryl sulfate (SLS), sodium laureth sulfate (SLES), sodium carbonate (washing soda), sodium hydroxide (lye). Some of these are tolerable in small amounts; high concentrations used regularly are the problem.
Boron / Borax
Borax (sodium borate) is a common "natural" cleaning booster, but boron accumulates in soil and becomes toxic to plants at relatively low concentrations. California's greywater guidelines specifically call out boron as a compound to avoid. Do not use any detergent containing borax, boric acid, or sodium borate in a greywater system.
Chlorine Bleach
Chlorine bleach kills the soil bacteria and fungi that plants depend on. It also creates chlorinated compounds (chloramines, trihalomethanes) when it contacts organic material, some of which are harmful to plants at low concentrations. Never run a load treated with chlorine bleach through your greywater system — always redirect those loads to sewer.
Optical Brighteners
These UV-reactive compounds make fabrics appear whiter under fluorescent light. They're persistent in soil environments and are considered moderately harmful to aquatic organisms and soil invertebrates. They don't biodegrade well and accumulate over time. Avoid detergents that list "fluorescent whitening agents" or "optical brighteners."
Phosphates
Phosphates have been banned from residential laundry detergents in most U.S. states since the 1990s, so this is less of a current concern — but verify your detergent is phosphate-free, particularly if you're using commercial-grade products.
Greywater-Safe Brands
| Brand | Product | Notes |
|---|---|---|
| Oasis | Laundry Liquid | Specifically formulated for greywater. Low-sodium, plant-based. The gold standard — used in California's original greywater pilot programs. |
| ECOS | Free & Clear | Widely available, biodegradable, no SLS or optical brighteners. Good all-around choice. |
| Seventh Generation | Free & Clear | No fragrances or dyes, plant-derived surfactants. Avoid their "Blue" variants which contain optical brighteners. |
| Charlie's Soap | Laundry Powder | Very low-residue formula. Rinses clean with minimal surfactant load reaching greywater. |
| Molly's Suds | Original Powder | No SLS, no bleach, no borax. Small brand but well-regarded in greywater communities. |
| Branch Basics | Concentrate | Truly free of problematic ingredients. Expensive but highly concentrated — cost per wash is competitive. |
How to Transition Your Laundry Routine
If you're switching from conventional to greywater-safe detergent, a few tips:
- Use up your current detergent (or donate it) before switching — don't mix products
- Run 2–3 loads with your new detergent to sewer first, to flush any residual conventional detergent from your machine's drum and dispenser
- Follow dosing instructions carefully — greywater-safe detergents are often more concentrated and less foam means better washing, not less
- Separate "problem loads" mentally: use sewer for loads with bleach, diaper water, heavily soiled work clothes, and wash those loads first if your machine tends to carry soap residue
A quick way to check if a detergent is greywater-compatible: look at the pH and sodium content in the Safety Data Sheet (SDS), available on the manufacturer's website. Target: pH 7–9 (neutral to mildly alkaline) and sodium content under 5% by weight. Many greywater-safe brands publish this data proactively.