Composting toilets are legal in California, but with a condition that catches most buyers off guard: in nearly every county, a composting toilet can only supplement an approved wastewater system, not replace one. Your showers, sinks, and laundry still produce graywater that has to drain somewhere legal, so a sewer hookup or permitted septic system is almost always still required. On top of that, the unit itself needs a local permit, and the composted end product has to be disposed of according to specific rules.
You Still Need Sewer or Septic
Most California jurisdictions treat a composting toilet as an accessory to a conventional wastewater system, not a standalone solution. Humboldt County’s code is explicit: waterless toilets “may replace a flush toilet and will be an accessory to, and not a replacement for, an approved OWTS.”1Humboldt County. Land Use Program OWTS means onsite wastewater treatment system, which is the technical term for a septic system.
The reason is simple. A composting toilet only handles what goes into the bowl. Every other fixture in your house still produces wastewater that needs legal disposal through a sewer line or a permitted septic system. If you’re building off-grid and hoping the composting toilet eliminates all wastewater infrastructure, you’ll still need, at a minimum, a graywater disposal plan approved by your county.
California has its own graywater rules that come into play here. Graywater covers wastewater from showers, bathroom sinks, bathtubs, and clothes washers; kitchen sink and dishwasher water is excluded as too contaminated. A simple “laundry to landscape” system that routes washing machine water straight to outdoor irrigation without altering household plumbing doesn’t require a permit under the California Plumbing Code. Anything that cuts into drainage plumbing, uses a pump, or includes a storage tank does.
Treat the installation as two projects: approval for the toilet, and a legal destination for the rest of your household wastewater. County health departments want to see the full picture before signing off.
Pick an NSF/ANSI 41 Certified Unit
The smoothest path to approval is choosing a model certified to NSF/ANSI Standard 41, the national standard for non-liquid saturated treatment systems. Certified units are independently verified against six performance requirements, including that they produce no offensive odors and that composted output meets bacterial content limits.2NSF. Composting Toilets Look for the NSF mark on the product itself, not a manufacturer’s claim of compliance.
Non-certified systems can sometimes be approved, but the burden shifts to you. Your local authority may require humus samples from the first treatment cycle to be sent to a certified lab before any material can be removed. The humus must not exceed 65 percent moisture content by weight and must contain fewer than 200 fecal coliforms per gram. An NSF-certified unit skips most of that testing because the certification already covers those benchmarks.
Getting the Local Permit
Your county health department and the city or county building department share jurisdiction over composting toilet installations. In San Francisco, the Department of Building Inspection’s Plumbing Inspection Division handles the installation permit, and the Department of Public Health weighs in when the toilet is going into a park, commercial space, or other public setting.3San Francisco Public Utilities Commission. Composting Toilets Most counties follow a similar split.
The practical sequence looks like this:
- Call both departments before buying equipment. Some counties keep lists of pre-approved systems or impose requirements beyond the state code.
- Submit an application that includes a site plan showing where the unit will go, the manufacturer’s specifications, and a waste management plan describing how you’ll handle the end product. Permit fees typically run a few hundred dollars; Sonoma County, for instance, charges just over $300 for a standalone plumbing permit.4Permit Sonoma. Waterless Toilets – Frequently Asked Questions
- Schedule an inspection after installation. The inspector verifies the unit matches your approved plans and meets ventilation, sealing, and access requirements.
Rules vary meaningfully from county to county. Humboldt updated its local code in 2018–2019 to explicitly accommodate composting and incinerating toilets as accessories to an approved septic system.1Humboldt County. Land Use Program Other counties don’t have provisions that clear, which is why the opening phone call matters.
Rules for the Finished Compost
Disposal is the most tightly regulated part of owning a composting toilet, because improperly handled human waste compost poses real public health risks. The entire composting process exists to destroy pathogens and reduce infection risk to acceptable levels.5United States Environmental Protection Agency. Water Efficiency Technology Fact Sheet – Composting Toilets
The finished material must either be buried on your property around non-edible plants and tree roots, or removed by a licensed septage hauler in accordance with local regulations.5United States Environmental Protection Agency. Water Efficiency Technology Fact Sheet – Composting Toilets It cannot be used on vegetable gardens or fruit trees. Use is restricted to ornamental landscaping and non-food-producing plants. Some jurisdictions go further. In San Francisco, the waste must be hauled and discharged by a California state-licensed waste hauler with a permit to discharge at one of the city’s wastewater treatment plants.3San Francisco Public Utilities Commission. Composting Toilets
One boundary worth drawing: composting toilet humus is separate from the organic waste collected under California’s SB 1383 program. Green bins are for food scraps and yard trimmings.6CalRecycle. Statewide Mandatory Organic Waste Collection Human waste cannot go in those bins.
If your jurisdiction requires lab testing of the humus before removal, the property owner has to retain the test records and produce them for authorities on request. When you sell, those records should transfer to the new owner.
What Happens If You Skip the Permit
Installing without a permit creates problems well beyond a code violation notice. If a licensed contractor does the work without pulling permits, the Contractors State License Board can impose civil penalties of up to $5,000 per violation, require the contractor to pay all permit fees and local penalties, or suspend or revoke the license.7Contractors State License Board. Filing a Building Permit Violation Form
For the homeowner, local building code violations are typically treated as misdemeanors under municipal codes, with fines that commonly reach $1,000 and potential jail time of up to six months. Prosecution at that level is rare for residential plumbing. The more practical consequences: your county can order the system removed, and an unpermitted composting toilet routinely surfaces during inspection and complicates a home sale.
San Francisco’s Public Utilities Commission warns that improper installation and use of a composting toilet may negatively impact public health, and mishandling the compost can carry serious consequences.3San Francisco Public Utilities Commission. Composting Toilets Pulling the permit upfront is cheaper and simpler than dealing with enforcement later.