Can I use shower water on my garden? Shower and sink graywater in Sonoma County

By The Downspout · Posted Oct 25, 2026 · 13 min read

Yes, with a permit. California lets you send shower, bathtub and bathroom sink water to trees and shrubs. The simplest way is a branched drain: a valve on the drain, and sloped pipes that let gravity carry the water to wood chip basins around plants. From June to September, a family's showers make nearly 4,900 gallons, about three times what the washer makes. Outside city limits, ask Permit Sonoma, the county's permit office, at (707) 565-1900. In a city, ask your building department.

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In an Oakland house, the drain pipe from an upstairs shower ran in plain sight through an unfinished laundry room below. One short piece of the old cast iron pipe came out. A 3-way valve went in. It has one pipe in and two pipes out, so you choose where the water goes.^[1]

Now the shower water can go to the sewer, or out through a new pipe to an apple tree, a passion fruit vine, a tree tomato and a row of climbing beans. An estimated 25 gallons a day. The parts cost about $200.^[1]

That is a branched drain, the simplest way to put shower water on a garden. It has no pump, no filter and no electricity. Gravity does the work.^[2]

It matters here because of when we need it. Santa Rosa gets about half an inch of rain from June to September in a normal year, and that is when the hose comes out.^[3] Meanwhile a family's showers send more water down the drain than its washing machine does.

Below: how much water that is, how the system works, what the county's permit takes, how big the mulch basins must be in clay, what it costs, and whether it pays.

Showers make more garden water than the washer

Graywater is the used water from showers, bathtubs, bathroom sinks and washing machines. It is not water from toilets, kitchen sinks or dishwashers.^[4]^[5]

Many people start with the washer, through a laundry to landscape system, a hose from the washer to mulch basins. Look at the blue bar: the showers make about 2½ to 3½ times the washer's water, whichever washer you have.

Our calculation for an average family, June 1 to September 30. Showering adds up to nearly 40 gallons a day.^[6] The washer runs about 100 loads in those months, at 14 or 20 gallons a load.^[7] Data and method.

In plain terms: for an average family, the shower makes more graywater than the washer. The catch is that it is harder to reach. The washer has a hose you can move. The shower's drain is a pipe inside a wall or under a floor.

How a branched drain works

Follow the water from the shower down to the trees.

Drawn from the San Francisco Graywater Design Manual.^[2]

The valve goes in the drain pipe. Leave the shower's own drain parts, the trap (the U-bend that holds water to block sewer smells) and the vent (the pipe that lets air into the drain), as they are. The valve goes below them, before the pipe meets the toilet or kitchen sink drain, so no toilet water can reach the garden. Label which way is garden and which is sewer.^[2]^[8]
The pipe always runs downhill. Standard 1½ or 2 inch drain pipe drops at least ¼ inch every foot, a 2 percent slope. So the plants must sit lower than the shower.^[2]
Splitters share the water. A double ell, a splitter fitting with two outlets side by side, cuts the flow in half. Each half can be split again.^[2]
Each line ends in a mulch basin. That is a shallow pit around a tree or shrub, filled with wood chips. The water comes out at least 2 inches under the surface of the mulch, or under a cover, so no one touches it.^[2]^[9]

Two limits to know.

Flat ground: the pipe keeps dropping ¼ inch a foot, so the far outlets end up deep. In one flat Richmond yard, where the pipe also had to pass under a sidewalk and a water line, the far outlets ended up 12 to 18 inches down. The installers expected the young trees to need extra water until their roots reached it.^[10]
Plants uphill: you need a pumped system with a holding tank instead. It costs more and uses electricity.^[2]

What does the permit take in Sonoma County?

California's plumbing code, the state rules for pipes and drains, lets a washer-only system skip the construction permit if it needs no change to the house plumbing and no pump.^[9] Permit Sonoma still lists a building permit for washer systems.^[11] Any system that takes water from a shower or sink needs a permit.^[4]

Almost every home's system counts as a simple system, one that handles 250 gallons a day or less.^[9] That matters because the permit steps below are the ones for a simple system.

To estimate a home's graywater, the code counts 2 people for the first bedroom and 1 more for each added bedroom, at 25 gallons a day per person from showers, tubs and bathroom sinks.^[12] So a 3-bedroom house counts as 4 people and 100 gallons a day. Even a 5-bedroom house with the washer hooked up too comes to 240 gallons a day, by our math (data and method). The code also lets you use your water bills instead of the bedroom count.^[12]

Outside city limits: Permit Sonoma, the county's permit office, lists two permits for every simple system: a building permit and a septic permit, plus a review of your design and an inspection. Its well and septic team handles graywater. The county lists the septic permit with no exception for homes on a sewer, so ask about it either way.^[11] Call (707) 565-1900.^[4]
In a city: the city handles graywater, not Permit Sonoma. Cities can set their own rules, as long as they meet or go beyond the state code. Ask your city's building department.^[4]^[9]
Your water utility: ask whether you need a backflow device at the meter, a valve that keeps used water from flowing back into public pipes.^[4]

Plan the spots before you dig. The plan below shows the state code's minimum distances for mulch basins, as Permit Sonoma and the San Francisco manual list them.^[13]^[2]

2 feet from the house, and 1½ feet from a neighbor's property line.
100 feet from a well, creek or lake.
5 feet from a septic tank, and at least 4 feet from a leach field, the buried pipes that spread septic water into the soil.
10 feet from a public water main.

The water must soak in, never pool, run off or reach a storm drain or creek.^[9] The bottom of each basin must sit at least 3 feet above the water table, the level where the ground is already full of water.^[2] When the winter rains soak the ground, turn the valve to the sewer.^[2] Our guide to wet yards and French drains explains why many lots here stay soggy all winter.

Exterior of a single-story home with brick wainscoting, a concrete walkway, and a bare dirt yard with mulch. — A one-story house with a mulched yard. Graywater basins go at least 2 feet from the house, around trees and big shrubs.

How big do the mulch basins need to be?

The code sizes the basins by soil, because clay drinks slowly. A 3-bedroom house counts as 100 gallons a day. Here is how much mulch basin that needs on each soil. Watch the blue clay bars stretch.

From the California Plumbing Code's soil table.^[14] If your soil type is not in this chart, a percolation test, which times how fast a hole drains, sets the size.^[14]

Clay is common here. About 7 in 10 acres of the county's soil takes in water slowly or very slowly, by our count in the French drain guide.^[15] Not sure of yours? Ask Permit Sonoma or your city which soil test it accepts for your lot.

A worked example. The 3-bedroom house above sends 100 gallons a day to clay with a little sand. It needs 120 square feet of mulch basin. That is six basins of 4 by 5 feet, around six trees or big shrubs.^[14] On sandy loam, 40 square feet would do.

What to water, and what to wash with

Water trees, shrubs and vines. Branched drains suit fruit trees, big shrubs and other large perennials.^[2]
Skip root crops. No carrots or potatoes, and nothing whose edible part touches the soil.^[8] UC Master Gardeners list unstaked tomatoes among crops to avoid, so stake them.^[16]
Send it to other trees before citrus and avocado. A small Colorado State University study found most plants were not sensitive to graywater, but citrus and avocado trees were.^[17] UC Master Gardeners in Alameda County do list citrus as a good graywater tree, so this one is unsettled.^[18]
Check the labels on soaps and shampoos. Skip any with sodium or boron (borax). Both can harm soil and plants.^[16]^[18]
Turn the valve for bleach and harsh cleaners.^[18]^[9]
Plan for vacations. Most simple systems only water while you are home making graywater.^[2] Water those trees another way while you are away.

What it costs, and does it pay?

Parts for a one-shower branched drain ran about $150 to $350 in 2018, so expect more now. The Oakland system above was about $200. An optional motor lets you flip the valve with a switch, handy when the valve sits in a crawlspace.^[1]^[10] With a professional, costs run from a few hundred dollars to a few thousand.^[2] Add permit fees; ask Permit Sonoma or your city.

The case for it. Greywater Action, a group that teaches and promotes graywater building, studied 83 systems in the Bay Area, Monterey Bay and Santa Rosa areas. After the systems went in, water use fell by an average of 17 gallons a person a day, about 14,565 gallons a year per household. They found no harm to soil or plant health. The water suited long-term watering as long as households avoided products with sodium or boron.^[19]

The case for caution. That study comes from people who build and promote these systems. The Colorado State team studied seven homes in four states, funded by a water research foundation and a soap industry group. In early results reported in 2012, they found salts in the soil can creep up over time, though not to levels that hurt plants.^[17] And the savings only show up if you would have watered those trees anyway.

Rebates. Petaluma, up to $125, and Healdsburg, $60, pay only for laundry to landscape systems.^[20]^[21] Santa Rosa Water describes its graywater rebate as one for washer systems. Santa Rosa lists no rebate just for shower systems. Its Sustained Reduction Rebate is for projects without their own rebate: if one cuts water use and wastewater flow every month, you may qualify for $400 for every 1,000 gallons it saves. Ask whether a shower system counts. Call Santa Rosa Water at 707-543-3985 before you start, since every Santa Rosa rebate needs a visit first.^[22] More on our rebates page.

Our take: if your washer is easy to reach, start there. It is cheaper, and the county asks for less. If your bathroom sits uphill of trees you water every summer, the shower is worth the permit, because it makes about three times the water.

Not ready for any of it? Put a bucket in the shower while the water warms up, and carry it to a plant.^[18] That is clean tap water, so none of the graywater rules apply.

What it means for the river

More than 600,000 people in Sonoma and Marin counties rely on Russian River water delivered by Sonoma Water. Threatened and endangered steelhead, coho and Chinook salmon rely on the same water.^[23]

Our view: your shower can help the river. If your tap water comes from Sonoma Water, shower water on a fruit tree in August is water the river does not have to give up in the dry season. On a well, it is groundwater you leave in the ground. The code's 100 foot distance from creeks, and its ban on runoff, keep that water out of the creeks themselves.^[13]^[9]

What it means for you

First, make one call: Permit Sonoma outside city limits, your city's building department inside them.
Look under the bathroom. Can someone reach the shower drain from a crawlspace or basement? Are the trees downhill?
Before you buy parts, ask which soil test your permit office accepts, and measure the ground around the trees you want to water. On clay, figure about 120 square feet of basin for every 100 gallons a day.
Flip the valve to the sewer when the winter rains soak the ground.

Next: start with the washer in our laundry to landscape guide, or find a graywater installer in our directory. They are listings, not recommendations.

Photos by Devan Hemmings unless noted.

Sources

Checked 2026-10-25. Rules and programs change. If something here is out of date, the source above wins. Spot an error? See our corrections policy.