Essential Guide to Grey Water Reuse Systems for Gardening in California [2025]

Setting up a grey water reuse system for gardening or landscaping is a smart choice as a California homeowner. After all, you’re no stranger to drought cycles and rising water costs. Finding creative ways to nourish your yard while conserving water is more important now than ever.

Grey water recycling in the garden is one of the most sustainable landscaping solutions you can choose, and it goes hand-in-hand with water-wise gardening.

In this guide, we'll walk you through the following:

●      What grey water is

●      How to reuse grey water legally and safely in California

●      How grey water can support beautiful, drought-friendly landscapes.

●      Easy ways to get started

What is Grey Water?

Grey water (also known as “gray water”) refers to gently used water from bathroom sinks, showers, bathtubs, and washing machines. Unlike "black water" from toilets, grey water is relatively clean and can be reused for outdoor irrigation with a few smart precautions.

Grey water reuse is a simple, powerful step toward a more water-wise garden — helping you significantly reduce your household water use while providing a steady source of hydration to your plants.

“Laundry to Landscape” (L2L) graywater system example from Valley Water

Yes, grey water systems are legal in California — and encouraged! Under California’s plumbing codes, simple systems like "laundry-to-landscape" don't even require a permit, provided they meet basic guidelines.

If you're planning a more complex grey water recycling system (like one with pumps or storage tanks), you’ll probably need a permit and will need to follow your local building codes.

California Grey Water System Codes

Since 2009, the California code does not require a permit or inspection for washing machine systems that do not alter the existing plumbing, as long as installers follow key guidelines:

• Include an easy way to direct flow back to the sewer/septic (e.g., a labeled 3-way valve).

• Send greywater only to irrigate landscape plantings.

• Keep the water on the same property it is produced and follow setback requirements.

• Provide a maintenance manual.

• Discharge greywater under a 2-inch cover of mulch, plastic shield, or stones.

  
  

Implementing a grey water system in California is not only environmentally beneficial but also legally supported and potentially cost-effective. Here's what homeowners need to know:

Cost Implications of Grey Water Reuse Systems

The cost of installing a gray water system can vary widely based on complexity. 

Grey water systems can be adapted to meet different household and landscape needs. 

They work especially well with fruit trees, and some drought tolerant shrubs, perennials, grasses and groundcovers, making them a great water source for California’s gardens. Grey water reuse also supports sustainable irrigation practices, with the use of mulch basins.

Curious about how much water you could save by converting your landscape to a native garden? Explore our Water Savings Calculator.

Want to see the big picture?

Grey water systems aren’t just practical at the home level — they’re also part of a larger shift toward smarter, more sustainable water use across cities and states.

The National Academies of Sciences highlights how grey water and stormwater reuse can create long-term economic and environmental benefits when adopted more widely. Now that we’ve covered how practical and accessible grey water systems really are, let’s dive into how you can get started in your own yard.

Reusing grey water in your yard can be simpler than you think — but there are a few smart steps to make sure you set yourself up for success.

If you’re considering reusing laundry water in your landscape, here are the essential guidelines to follow:

• Choose a laundry-to-landscape system. This is the simplest, most widely used method for reusing greywater at home.
• Stick with plant-friendly soaps. Look for products labeled as “biodegradable,” “greywater-safe,” and free of boron, salts, or chlorine bleach.
• Direct greywater into mulch basins. California law requires that greywater be distributed into mulch basins around trees, shrubs, or other perennial plants. The basins should always be covered with at least 2 inches of mulch.
• Never spray greywater. Spraying onto plants or edible parts is not only unsafe—it’s also illegal. Properly designed systems will prevent this.

By following these basics, you’ll keep your greywater system safe, effective, and compliant while giving your landscape an eco-friendly boost.

Different homes (and gardens) call for different systems. Some options include:

●      Laundry-to-Landscape Systems: Route your washing machine water directly to the garden. No permit, low cost.

       ●      Simple Branched Drain Systems: Gravity-fed systems that split bath or shower water to different parts of your yard.

        ●      Pumped Systems: Needed if your landscape isn’t downhill from the source. Often requires a tank, a pump, and a permit.

●      Constructed Wetlands: Let plants naturally filter the grey water before reusing it — best for larger or multi-source setups.

For most households, "Laundry to Landscape" is the easiest to implement.  

Before you design your system, figure out where your grey water will come from.  If you have a washing machine, check where the drain hose is.  That is your source of greywater.  It is the most suitable for installation if the washing machine is near an exterior wall and the garden to water, and above the crawl space. 

Other sources of greywater include showers and bathtubs.  Not sure what you can reuse? Check out your local regulations or California Water Boards guidance.

Designing your system is about matching water supply with plant demand and planning an efficient route.

1. Calculate Your Greywater Supply

Start by estimating how much greywater your washing machine produces each week.  Ask yourself:

• How much water does your washing machine release per cycle? (check the manual or look it up online) 
• How often do you do laundry? (how many cycles per week?)

Formula: Weekly greywater = water per cycle × number of cycles per week

This number is the total water available for your plants.

2. Estimate Plant Water Needs

Next, compare your supply to your plants’ needs.  This ensures your greywater system delivers enough water—without over- or under-watering.

For reference, here shows the amount of water per week required for optimum growth in different areas.

3. Map the Greywater Route

Plan how the water will move from your washing machine to your plants.

• Draw a layout: mark where your laundry machine is, where the pipes will run, and where the outlets (mulch basins) will be placed.
• Cover all target plants: make sure the route reaches every plant you want to irrigate.
• Design outlets: place multiple outlets along the route so the water distributes evenly.

Example:

One greywater line loops around four plants, with five outlets. Each outlet delivers water into a mulch basin at the base of a plant.

Here shows an actual mulch basin, and the outlets (purple cover).

Step 4: Select the Right Plants

Grey water works best with these plants.

• Fruit trees:  Lime, Mayer Lemmon, Orange, Apricot, Peach, Persimmon, pomegranate, Common Fig
• Established shrubs: Japanese Maple, Orange Grape, Golden Currant, Coyote brush, Wax Myrtle
• Hardy perennials and herbs Rosemary, Lavender, Thyme,

Grey water is fine for non-edible parts of plants, but don't let it touch any leafy greens, root vegetables, or fruits you’ll eat raw. 

Want to dig deeper? Check out Greywater Action: Greywater and Edible Plants.

Once your greywater system is in place, the next step is getting that water safely to your plants. In most laundry-to-landscape systems, the water flows directly into mulch basins around trees or shrubs. The good news: these simple systems usually require little or no filtration. More complex setups with pumps or holding tanks, however, may need additional filters to protect both your garden and your hardware.

Filtering In Direct-to-Mulch Systems

For direct-to-mulch systems, the soil itself—protected with a layer of mulch—is the most effective filter.

• A mulch basin is essentially a shallow depression filled with 2+ inches of coarse mulch at the outlet point.
• As greywater enters, the mulch and soil capture particles like lint and hair, breaking them down over time.
• This not only keeps water clean as it infiltrates but also adds organic matter back into the soil, improving its structure and fertility.

✅ Tip: Refresh mulch annually to maintain good filtration and odor control.

Graywater discharge point: illustrating (D) and (E) from Chapter 15 of California Plumbing Code

Best Methods for Greywater Delivery

The goal is to apply water directly to the soil where plant roots can absorb it—never on leaves, fruits, or edible portions.

Recommended methods:

• Mulch basins around trees and shrubs
• Subsurface irrigation for more advanced systems

Avoid spraying grey water onto foliage, especially on anything you plan to eat. Always cover discharge points with mulch to help filter particles and minimize odors.

? Tip: Start with one simple zone (like fruit trees) and expand over time!

Quick answer: It can be — with the right strategy.

Grey water is fine for non-edible parts of plants, but you don't want it touching leafy greens, root vegetables, or fruits you’ll eat raw. It’s great for:

●      Fruit trees (just water the root zone)

       ●      Tomato plants (aim water below the fruit)

●      Woody herbs like rosemary, lavender, and thyme

Want to dig deeper? Check out Greywater Action: Greywater and Edible Plants.

Why Choose Grey Water Systems for Your California Garden?

Choosing to reuse grey water in your home garden means:

●      Conserving water when every drop counts

       ●      Lowering your water bills

       ●      Keeping your garden green even in dry spells

       ●      Supporting native and drought-tolerant plants

●      Investing in sustainable irrigation for long-term resilience

Whether you're dreaming of a colorful, pollinator-friendly garden or a peaceful shady retreat, backyard water-saving systems like grey water reuse are a smart move.

Design Your Drought-Friendly Dream Garden

At Water Efficient Gardens, we’ve helped Californians save nearly 3 million gallons of water by converting their yards to native, water-efficient gardens.

Schedule a Free Consultation to see how we can help you design a landscape that supports grey water reuse in your California home — and thrives through every season.