Greywater at Home: How to Reuse It Safely (and Why Your Softener Matters)

Reusing Greywater at Home: What's Allowed, What's Safe, and Where Your Softener Fits

Every load of laundry and every shower sends water down the drain that could still do one more job outside. That used water is greywater, and with the right setup it can soak into the root zone of your shrubs and fruit trees instead of heading to the sewer.

The numbers explain the interest. The U.S. Environmental Protection Agency's WaterSense program says the average American family uses more than 300 gallons of water a day at home, and roughly 70 percent of that happens indoors. Outdoor water use accounts for about 30 percent nationally, and it can run much higher in drier parts of the country. Some of the water you're already using indoors can take over part of that outdoor job.

Here's the short version. Greywater is used water from showers, bathtubs, bathroom sinks and clothes washers. Send it under mulch to landscape plants, keep it on your own property, use it the same day and keep it off food crops whose edible parts can touch the soil. Check your state's rules before you touch a drain line. And if your home has a salt-based water softener, sort out the sodium first, because that's what can quietly wear down your soil.

What Counts as Greywater, and What Doesn't

The Arizona Department of Environmental Quality (ADEQ) gives a clear working definition in its homeowner guide to gray water: wastewater collected separately from your sewage flow that "originates from a clothes washer, bathtub, shower or sink, but not from a kitchen sink, dishwasher or toilet." Water from toilets, kitchen sinks and dishwashers is black water, and ADEQ says it shouldn't be reused in the home "because of high risk of contamination by bacteria, viruses and other pathogens."

Even the "yes" drains carry more than water. ADEQ notes that greywater may contain fats, oils, grease, hair, lint, soaps, cleansers and fabric softeners. It can also carry "elevated levels of chlorides, sodium, borax and sulfates and have a high pH (is alkaline) that may be harmful to some plants." Keep that sentence in mind, because most of the choices below come back to it.

One small thing people mix up: some guides list a bucket of shower warm-up water alongside greywater options, but that water hasn't been used yet. It's plain tap water, so you can use it anywhere you'd use water from the hose.

Check Your State's Rules Before You Plumb Anything

Greywater rules are set by states and local building departments, and they don't line up neatly. Two Western states with well-documented homeowner rules show how different "allowed" can look.

California: Laundry-to-Landscape Without a Permit

According to UC Master Gardener guidance on grey water, washing machine systems in California "that do not alter the house plumbing can be built without a construction permit as long as certain guidelines are followed." Valley Water, the Santa Clara County water agency, publishes those conditions from Chapter 15 of the California Plumbing Code. Among them:

• If your city or county requires it, you've notified the local building or planning department about where the system goes and how it's installed.
• No connection to the potable water system and no added pump. The code notes that the washer's own pump isn't considered part of the greywater system.
• A clearly labeled, easy-to-reach control lets you send the flow either to the yard or to the building sewer.
• The greywater stays on the site where it's generated.
• "Ponding or runoff is prohibited and shall be considered a nuisance."
• At least 2 inches of mulch, rock or soil, or a solid shield, covers each release point.
• Water from diapers or similarly soiled or infectious garments goes to the building sewer instead.
• No hazardous chemicals in the water.
• The owner gets an operation and maintenance manual.

Shower and tub systems usually mean cutting into drain lines, which takes them outside that washer-only exemption. Plan on talking to your building department first.

Arizona: A General Permit You Don't Apply For

Arizona covers household greywater under a Type 1 general permit. ADEQ says it "requires no formal notification to the department, no review or design approval, and no public notice, reporting or renewal." You still have to follow the 13 best management practices in the state's brochure. The key ones:

• Private residential use only, on the site where the greywater is generated.
• Apply it by drip or flood irrigation. Spraying is prohibited.
• Flow must be less than 400 gallons per day.
• Groundwater must be at least five feet below the surface where you use it, and you can't use it in a wash or drainage way.
• No surface irrigation of plants that produce food, except citrus and nut trees.
• No hazardous chemicals such as antifreeze, mothballs or solvents, and no wash water from greasy or oily rags.

ADEQ also notes that, in general, no city, town or county may limit greywater use that the general permit allows.

Everywhere Else

Don't assume either state's approach carries over to yours. A washer system that needs no construction permit in California could need a permit, an inspection or an approved design somewhere else. New Mexico State University's greywater guide puts it plainly: "Be sure to obtain all necessary permits before installing a greywater system." Your local building department or state environmental agency can tell you what applies at your address, and your county extension office is a good place to ask about local soils and plants.

The Simplest Ways to Start

Most homeowners begin with laundry, and it's easy to see why. The washer already pushes its rinse water out through a drain hose, so a laundry-to-landscape system connects that hose to a labeled diverter valve. Each load can then go either to a dedicated line to the yard or to the sewer. The UC Master Gardener guidance describes where it should land: "the water should enter the landscape at the dripline of plants with a good cover of mulch," with each discharge point under 2 inches of mulch, stones or a plastic shield. It also says greywater "must not be used in a sprinkler system."

The same UC guidance says greywater "can be safely used to water landscape plants and orchard trees." Valley Water adds that decorative trees, fruit trees, shrubs, vines and hardier native plants perform well. New Mexico State University's guide says to "use greywater only on well-established plants, not seedlings or young plants," and warns that plants that thrive only in acid soil shouldn't get greywater, which is alkaline. Plan several mulched outlets rather than one, because the same guide advises you to "disperse greywater over a large area, and rotate with fresh water to avoid buildup of sodium salts."

If you're carrying water by hand from a tub or washer, the same rules apply. Pour it onto the soil under mulch, not over leaves, and use it that day rather than letting a bucket sit.

If You Have a Water Softener, Start Here

This is where the water treatment inside your house decides what your plants get. A conventional salt-based softener removes calcium and magnesium by exchanging them for sodium ions. Valley Water explains the scale of it simply: "The harder the water, the more sodium or potassium respectively is added to effect softening." If your softener feeds the washer and the showers, every drop of greywater from those sources carries that added sodium outside.

Sodium is the problem ingredient for soil. Penn State Extension's guide to interpreting irrigation water tests, written for growers, says "removal of hardness by using a water softener with sodium chloride often leads to issues of elevated sodium." It treats sodium above 50 mg/L as a possible toxicity risk for sensitive plants, particularly in recirculating irrigation systems. It also explains that when water high in sodium and low in calcium and magnesium is applied often to clay soils, the sodium tends to push calcium and magnesium off the clay particles, breaking down soil structure and reducing how well water soaks in. Softened water fits that description, since the softener has already traded its calcium and magnesium for sodium.

You don't have to give up soft water to use greywater. Valley Water's graywater resources suggest switching to a potassium-based softener, bypassing the clothes washer from the softened water, adding reverse osmosis, or looking at alternatives to conventional ion-exchange softeners. Here's how those options line up with common home setups:

Two more details matter. The softener's own regeneration discharge is concentrated brine, and Penn State lists water softening wastes among the sources of sodium in water, so leave it on its normal drain and never route it to the yard. And if you're switching salts, Valley Water says most household softeners need no equipment changes, but check your owner's manual for compatibility. Our guides to softener bypass valves and choosing softener salt walk through both steps. If you're weighing the salt-free route, our comparison of salt-free conditioners and salt-based softeners explains what each one actually does to hard water. For other uses of RO concentrate, see our guide to reverse osmosis waste water.

Your Laundry Products Matter Too

A softener isn't the only source of salt in greywater. Detergents and additives go straight to the soil with the rinse water. The UC Master Gardener guidance advises avoiding "products that contain sodium or sodium compounds, bleach, and/or boron," because they can create an alkaline soil condition that suppresses healthy soil life and that many plants tolerate poorly. Valley Water adds antibacterial compounds and fabric softeners to the list of ingredients that "can degrade the health of your landscape's soil over time."

Boron deserves a closer look, since plants react to it at very low levels. The same UC guidance groups landscape plants by tolerance:

• Low tolerance: prefer boron no higher than 0.5 to 1.0 mg/L.
• Moderate tolerance: can manage 1.0 to 2.0 mg/L.
• High tolerance: should handle 2.0 to 10.0 mg/L.

You can't easily measure boron in your rinse water at home, so the practical move is choosing boron-free and borax-free products, especially if your greywater goes to plants on the low-tolerance end.

Watch the word "softener" on laundry labels, too. Fabric softener is a different product from a water softener, and it belongs on the avoid list. New Mexico State University suggests skipping liquid fabric softener and detergents with softener built in, and using a softener sheet in the dryer instead.

Greywater Safety Rules That Don't Bend

The details vary by state, but these health and soil basics run through the official guides cited here:

• Outdoor irrigation for a simple home system. Never drink it, cook with it, bathe in it or wash dishes with it. Plumbed indoor reuse, such as toilet flushing, is a different kind of system, so talk to your building department first.
• Keep it covered. Release it under mulch, rock or a shield, and never through a sprinkler. ADEQ prohibits spraying because of the potential for inhalation or drift.
• Avoid contact. ADEQ's first practice is to avoid human contact with greywater and the soil it irrigates.
• Keep it off food that touches soil. UC guidance says greywater "should not be used to grow vegetables if the edible portion may come in contact with the soil," naming crops such as carrots, lettuces, potatoes and strawberries, because it can contain bacteria and viruses that cause illness. Where your state is stricter, follow it: Arizona allows no surface irrigation of food plants except citrus and nut trees.
• No puddles, no runoff. It should soak in where you put it and stay on your property.
• Use it the same day. Don't store untreated greywater longer than one day.
• Divert the risky loads. Wash water from diapers or other soiled garments goes to the sewer, not the yard, so switch the diverter before you run those loads. Keep greasy or oily rags and anything carrying solvents, antifreeze or other hazardous chemicals out of your greywater entirely, and take leftover chemicals to a household hazardous waste drop-off rather than any drain.

Can a Water Filter Make Greywater Safe to Drink?

Not at home, and it's worth being clear about why. The UC Master Gardener guidance describes greywater as "untreated, non-disinfected household wastewater." Recycled water, as that same California guidance describes it, is a different product entirely: it "has been through three levels of treatment including filtration and disinfection," and even that water "should not be used for drinking, cooking, bathing or showering."

Home drinking water filters are built to treat water that's already delivered as drinking water, not household wastewater. The filters you'll see on greywater systems do a different job. ADEQ suggests one "to reduce plugging and extend the system's lifetime," so the lines and outlets keep flowing. Treat greywater as irrigation water from start to finish, and let the water treatment inside your home focus on what comes out of your taps.