Sourced from the State Water Resources Control Board OWTS Policy (Resolution 2012-0032, amended 2018 and 2023) and its published implementation guidance — last checked August 2026.
California Septic Guide — Free Tool
Which OWTS Tier Are You Under?
California’s OWTS Policy sets five tiers, and which one applies decides your siting standards, your flow ceiling, whether supplemental treatment is required, and whether you can add an ADU. The state publishes the framework but nothing that tells a homeowner where they land.
Directional guidance based on the State Water Board OWTS Policy and its published regional jurisdiction list. Your local agency makes the actual determination, and an approved Local Agency Management Program can set standards that differ from the statewide defaults. Confirm with your county before relying on this.
The Five Tiers
| Tier | Applies to | Max flow |
|---|---|---|
| Tier 0 Section 6 |
Existing systems that work properly and need no corrective action | 10,000 gpd |
| Tier 1 Sections 7–8 |
New or replacement systems under the statewide default standards. Applies where no LAMP is approved. | 3,500 gpd |
| Tier 2 Section 9 |
New or replacement systems under an approved Local Agency Management Program | 10,000 gpd |
| Tier 3 Section 10 |
Systems near impaired surface waters. Supplemental treatment may apply. | 10,000 gpd |
| Tier 4 Section 11 |
Systems that are failing and require corrective action | — |
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Tier 0 — Your Existing System
If you have a system that works and doesn’t need fixing, you’re in Tier 0. Most California septic owners are.
But Tier 0 has exclusions worth knowing. It does not apply to a system that is near an impaired water body subject to a TMDL, is covered by a local agency special provision, or sits within 600 feet of a water body listed on the Policy’s impaired waters attachment.
If any of those apply, you’re likely in Tier 3 instead — which carries additional treatment, monitoring and oversight requirements.
Tier 1 — The Statewide Default
Tier 1 covers new and replacement systems built to the Policy’s conservative statewide siting and design standards. It applies wherever a Local Agency Management Program has not been approved by the Regional Water Board.
Tier 2 — LAMP Counties
A Local Agency Management Program is a county or city program approved by its Regional Water Board. Where one exists, new and replacement systems are permitted under those local standards rather than the statewide default.
This is more consequential than it sounds. Under Section 9, a LAMP’s siting and design standards may differ from Tier 1 — and that can go either direction. Some LAMPs are more permissive because local soils and climate justify it. Others are stricter.
The flow ceiling also rises to 10,000 gpd.
See our guide to LAMP counties.
Tier 3 — The Expensive One
Tier 3 applies where a system sits near impaired surface water. Specifically: subject to a TMDL implementation plan, covered by a special provision in a LAMP, or located within 600 feet of a water body listed on the Policy’s impaired waters attachment.
Supplemental treatment may be required — treatment beyond a conventional tank and leach field, typically to reduce nitrogen or pathogens. That is the single largest cost variable in what a septic system costs in California.
Counties in Tier 3 areas have options: implement the Policy’s default Tier 3 requirements, a Regional Water Board approved Advanced Protection Management Program (APMP), or an approved TMDL implementation program.
See our Tier 3 guide, and note the 2023 change below.
Tier 4 — Failing Systems
Tier 4 covers systems requiring corrective action. The Policy names the indicators directly:
Surfacing effluent · wastewater backing up in plumbing fixtures · structural failure of a system component or pipe · significant groundwater or surface water degradation
Meeting any of those puts you into a corrective action process run by your local agency. It applies regardless of which tier you were in before.
Something That Changed in 2023
The April 2023 amendment to the OWTS Policy removed some water bodies from the impaired waters list.
The state’s own guidance is explicit about the consequence: systems located near water bodies removed from that list are no longer subject to Tier 3 requirements, unless the local agency has developed an APMP for the area.
So if you were told years ago that your property was in a Tier 3 area, that may no longer be true. See our guide to what changed.
Why This Is Confusing By Design
California doesn’t run septic permitting centrally. The State Water Board writes the Policy, nine Regional Water Quality Control Boards oversee implementation, and roughly 66 local agencies issue the actual permits.
That structure exists so local conditions can shape local rules — which is reasonable. The side effect is that a homeowner has no single place to look up what applies to them.
See our guide to who issues your permit.
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Frequently Asked Questions
How many OWTS tiers does California have?
Five, numbered Tier 0 through Tier 4. Tier 0 covers existing functioning systems, Tier 1 is the statewide default for new and replacement systems, Tier 2 applies in LAMP counties, Tier 3 covers systems near impaired waters, and Tier 4 covers failing systems. A lot of published guidance describes only three.
What is the Tier 1 flow limit?
3,500 gallons per day, the lowest ceiling of any tier. Every other tier allows up to 10,000 gpd. On a larger property in a county without a LAMP, that ceiling can be the binding constraint.
What puts a property into Tier 3?
Being within 600 feet of a water body on the OWTS Policy impaired waters attachment, being subject to a TMDL implementation plan, or being covered by a special provision in a LAMP.
What counts as a failing system in California?
Under Section 11, surfacing effluent, wastewater backing up in plumbing fixtures, structural failure of a system component or pipe, or significant groundwater or surface water degradation. Any one puts the system in Tier 4.
Can my tier change?
Yes. The April 2023 amendment removed some water bodies from the impaired waters list, and systems near a removed water body are no longer subject to Tier 3 unless the local agency has an advanced protection management program for the area.