Recycling Washing Machine Water (Greywater)

What is washing machine water (greywater) — and is it safe?

Greywater is household wastewater from everywhere except the toilet — such as water from the washing machine, shower and sink. Toilet water and kitchen/dishwasher water (which carries grease and food waste) counts as “blackwater” and is left out of these systems.^[3]

When a few conditions are met, laundry water is the most practical greywater source to reuse: the machine’s own pump pushes the water out, which cuts down on extra equipment. But keeping it safe comes down to your detergent choice, how long you store it, and where you send it (see “Safety and detergent rules” below).

Ways to recycle washing machine water

Depending on your budget and how much effort you want to put in, there are three basic methods:

1) Manual collection: The simplest route. You direct the machine’s drain hose into a bucket or container, or collect the rinse water yourself. You can carry this water out to the garden or pour it into the toilet cistern to use for flushing. It needs no equipment but takes effort, and the water must be used within 24 hours.

2) Laundry-to-landscape (L2L) diversion: The most popular permanent solution. We break it down in the next section.

3) Treatment/recycling system (“apparatus”): These systems filter, treat and store greywater. They make the water suitable even for indoor uses such as flushing the toilet — but installation and cost are high, and they usually call for professional fitting.

How does a laundry-to-landscape system work?

L2L is a simple system that sends laundry water straight to the garden without storing it:^[2]

1. A 3-way diverter valve is fitted to the machine’s drain hose, so you can send the water to the sewer or to the garden whenever you choose.
2. The machine pushes the water through a pipe to the garden using its own internal pump — no extra pump needed.
3. The pipe ends in mulch basins out in the garden (small holes filled with wood chips/mulch); the water reaches the plant roots below the surface.

In many areas this system needs no permit, and if you’re handy you can install it yourself for a few hundred dollars; professional installation is also an option.^[2] (Even so, confirm the rules in your own area — regulations vary from country to country.)

Where can you use recycled water — and where can’t you?

Suitable uses:

• Subsurface irrigation of ornamentals, shrubs, trees and lawn
• The root zone of fruit trees (without touching the fruit or leaves)
• Toilet flushing and outdoor cleaning (paving, courtyards)

Uses to avoid:

• Drinking, cooking or showering — never.
• Direct contact with root vegetables and edible parts (lettuce, carrots, etc.).^[1]
• Stored greywater (older than 24 hours) — it goes off, smells and grows bacteria.

Safety and detergent rules

What really makes greywater safe is what you put into it.

Other rules:

• Don’t store it for more than 24 hours; greywater breaks down fast. Use it fresh when you can.
• Apply the water below the surface; don’t spray it onto leaves or edible parts.
• Don’t use water from washing diapers, heavily soiled laundry, or a sick person’s clothes on the garden.
• To prevent salt building up in the soil, irrigate with fresh water now and then and spread the greywater over a wide area.
• Check the local regulations in your area.

How much water and money does it save?

Washing machines make up about 16% of a household’s wastewater.^[2] Water use per wash by machine type:

Source: Whirlpool water-usage guide.^[5] A home doing several washes a week can divert this water to the garden and save thousands of litres of drinking water a year — in dry regions, that’s a real gain for both the bill and the environment.

Frequently asked questions

Is laundry water safe for the garden? Yes — it’s safe if you use a greywater-friendly detergent, apply it below the surface, and use it within 24 hours.

Which plants can I water with it? Ornamentals, shrubs, trees and lawn; the roots of fruit trees. It shouldn’t go directly on root vegetables or edible parts.

Can I store greywater? Not unless it’s treated; don’t keep it longer than 24 hours, or it will smell and spoil.

Which detergent should I use? A biodegradable one with no sodium/phosphates/boron, and no bleach or fabric softener.

Do I need a permit? Simple laundry-to-landscape systems need no permit in many places; still, confirm your local rules.

Can it be used in the toilet? Yes, collected laundry water can be used to flush the toilet; treatment systems automate this.

Sources

1. Greywater Action — Greywater-Friendly Products & Plants. https://greywateraction.org/greywater-plant-friendly-products/
2. Watershed Management Group — Laundry to Landscape Greywater. https://watershedmg.org/services/home/greywater-kit
3. Alameda County Water District — Graywater / Laundry to Landscape. https://www.acwd.org/graywater
4. Modern Farmer — How to Irrigate with Graywater. https://modernfarmer.com/2017/03/laundry-garden-irrigate-graywater/
5. Whirlpool — How Much Water Does a Washing Machine Use? https://www.whirlpool.com/blog/washers-and-dryers/he-washing-machine-water-usage.html
6. Mother Earth News — Laundry-to-Landscape Greywater System. https://www.motherearthnews.com/sustainable-living/greywater-zm0z11zphe/