Greywater can be used for landscape irrigation, flushing toilets, and watering fruit trees, making it one of the simplest ways to cut household water use. Since greywater accounts for up to 75% of the wastewater a home produces, reusing even a portion of it can make a significant dent in your water bill and your environmental footprint.
Greywater is any household wastewater that doesn’t come from a toilet. That includes water from showers, bathtubs, bathroom sinks, and washing machines. In some states, kitchen sink and dishwasher water are classified separately (Utah, for example, treats kitchen water as blackwater) because of the higher grease and food particle content. So what counts as greywater depends partly on where you live.
Landscape and Garden Irrigation
The most common use for greywater is watering your yard. It works well for ornamental plants, shrubs, lawns, and fruit or nut trees. A typical setup routes washing machine water directly into the landscape through branched drain lines, delivering water at the base of plants right at the dripline. This is often called a “laundry-to-landscape” system, and in many states it requires no permit.
There are important ground rules. Greywater should never run through a sprinkler system, because aerosolizing untreated water creates a health risk. Instead, the water needs to soak into the soil at ground level. Every discharge point should be covered with at least two inches of mulch, stones, or a plastic shield to prevent direct contact and reduce odor.
Edible Plants: What’s Safe and What’s Not
You can use greywater on fruit trees and other crops where the edible part grows well above the ground. The risk comes when edible portions touch soil that greywater has passed through, because greywater can carry bacteria and viruses. That means you should avoid using it on root vegetables like carrots, beets, potatoes, radishes, and turnips. Leafy greens, lettuces, and salad crops are also off the list. The same goes for low-growing produce like strawberries, bush beans, cucumbers, melons, squash, unstaked tomatoes, garlic, and onions.
If you want to water a vegetable garden with greywater, stick to crops that fruit on tall, staked vines or trees where the harvest never contacts the soil surface.
Toilet Flushing
Using greywater to flush toilets is a proven indoor reuse strategy, but it requires a proper treatment system. Unlike outdoor irrigation, where soil acts as a natural filter, indoor reuse demands filtration, disinfection, and in some jurisdictions, dyeing the water so it’s visually distinct from tap water.
A typical system collects greywater from showers or sinks, runs it through a pre-filter to remove larger particles, stores it briefly, then pushes it through a finishing filter (usually rated at 5 microns or finer) before disinfecting it. Filters rated at 3 microns or smaller do a better job of catching parasites like Cryptosporidium and Giardia. After treatment, the water is piped to toilet tanks. These systems are more complex and expensive than a simple irrigation diversion, but they can offset a substantial chunk of indoor water use since toilet flushing is one of the biggest water draws in most homes.
Choosing the Right Soaps and Detergents
If your greywater is headed for the garden, the products you use in the shower and laundry matter. Plants and soil organisms are sensitive to certain chemicals that are common in household cleaners. The short list of ingredients to avoid:
- Sodium compounds and salts: These build up in soil over time and damage plant roots.
- Boron, borax, and sodium perborate: Boron is directly toxic to many plants, even in small amounts.
- Chlorine bleach: Kills beneficial soil microbes.
- Antibacterial soaps: Same problem as bleach, wiping out the microbiology your soil needs.
- Synthetic fragrances, artificial dyes, and parabens: These degrade soil quality and don’t break down easily.
Look for products labeled “biodegradable” or “biocompatible.” Plant-based liquid soaps and detergents without whiteners or softeners tend to be the safest choices. This is one of the simplest adjustments you can make, and it protects your soil long before you install any hardware.
How Much Water You Can Actually Save
Greywater makes up roughly 50% to 75% of total household wastewater by volume. Some estimates put it closer to 69% of all domestic water consumption. If your household uses 100 gallons of water per day indoors, somewhere between 50 and 75 gallons of that could qualify as reusable greywater. In homes with composting or dry toilets, that figure climbs to around 90%.
Even a basic laundry-to-landscape system can redirect 15 to 25 gallons per load of laundry. For a family running five or six loads a week, that’s over 100 gallons of irrigation water that no longer comes from the tap. In drought-prone regions, those numbers add up fast.
Storage and Timing
Untreated greywater should be used quickly. The organic matter and nutrients in it provide a breeding ground for bacteria, and pathogen levels rise the longer the water sits in a tank. The general best practice is to use greywater within 24 hours of collecting it. If your system includes a surge tank or storage container, it should have an overflow drain connected to an approved sewer or septic line so excess water doesn’t stagnate.
Storage tanks should be labeled “Caution: non-potable water. Not safe to drink,” secured so they can’t tip, and sized to handle peak flow from whichever fixtures feed them.
Keeping Your System Running
Greywater systems are low-tech, but they’re not maintenance-free. Filters and grease traps need regular cleaning to prevent clogs, especially if kitchen water is part of the system. In climates with freezing winters, you’ll want to drain all irrigation lines before cold weather sets in and restart the system in spring.
A basic seasonal checklist includes inspecting the surge tank, flushing distribution lines, checking mulch coverage over discharge points, and confirming that the overflow drain is clear. Most of this takes an hour or two a few times a year. The payoff is a system that runs reliably for years without expensive repairs and keeps a meaningful share of your household water working twice.