California · State Water Board OWTS Policy (Water Quality Control Policy for Siting
California's OWTS Policy sets a statewide floor, but counties administer the program under Local Agency Management Programs, and a county with an approved LAMP can set its own standards above the floor.
Minimum tank
One to three bedroom dwelling.
Design flow
Held two days for settling.
Cost index
Regional labour and permits.
Sets the design flow and the legal minimum.
Code sizes on bedrooms, not people.
Used to size the matching drainfield. Unsure? Sandy loam is the common default.
Everything, in one state. Coastal ranges with shallow rock and steep slopes, Central Valley clays and hardpan, Sierra granite, desert sands in the southeast. Slope limits and setbacks from surface water are frequently the binding constraint rather than soil.
Conventional trenches on suitable ground. Supplemental treatment is required in many jurisdictions where separation to groundwater is thin or the site is near impaired water bodies. Seepage pits persist in some counties and are prohibited in others.
| Dwelling | Design flow | Minimum tank | With disposal |
|---|---|---|---|
| 1 bedroom | 300 gpd | 1,200 gal | 1,450 gal |
| 2 bedrooms | 300 gpd | 1,200 gal | 1,450 gal |
| 3 bedrooms | 450 gpd | 1,200 gal | 1,450 gal |
| 4 bedrooms | 600 gpd | 1,250 gal | 1,500 gal |
| 5 bedrooms | 750 gpd | 1,500 gal | 1,750 gal |
The important thing in California is finding out whether your county has an approved LAMP. If it does, the county's standards apply, and they are often more restrictive than the statewide policy — particularly on setbacks, slope, and supplemental treatment triggers.
The state sets a floor. These California counties are where the largest septic populations sit, and where local requirements most often exceed it.
| County | What makes it different |
|---|---|
| Riverside | Large septic population; county program with its own standards |
| San Diego | Steep terrain and thin soils in the backcountry |
| Sonoma | Groundwater protection near the Russian River drives supplemental treatment |
| El Dorado | Sierra foothills; granite and slope constraints |
| Placer | Foothill development with shallow rock |
| Nevada County | Steep, rocky ground and strict setbacks |
A three-bedroom home at 150 gallons per bedroom produces 450 gallons per day of design flow. On sandy loam that needs roughly 750 square feet of absorption area. On clay loam it rises to about 2,250 square feet, and on clay a conventional field is usually not permitted at all. Run your own soil class through the drainfield calculator.
Many LAMPs require periodic inspection or an operating permit for advanced systems, with reporting to the county. Use the pump schedule calculator to work out the interval for your tank size and household.
Regional labour and permit costs in California run about 138% of the national baseline. Here is what typical installations land at for a three-bedroom home:
| System type | Typical installed cost in California | When it applies |
|---|---|---|
| Conventional gravity | $12,400 – $22,100 | Good soil, adequate depth to water |
| Chamber system | $13,600 – $25,400 | Alternative to gravel trenches |
| Mound system | $23,600 – $46,400 | Shallow water table or thin soil |
| Aerobic treatment | $19,800 – $39,800 | Clay soil or small lots |
| Tank pump-out (service) | $440 – $900 | Every 3–5 years |
Replacing an existing system costs more than these figures — old-system removal and re-permitting add to every line. The replacement cost calculator covers that case, and the cost estimator adjusts all of the above for your bedroom count and soil.
Verify before you build. The figures above are state minimums compiled for planning, drawn from State Water Board OWTS Policy (Water Quality Control Policy for Siting, Design, Operation and Maintenance of Onsite Wastewater Treatment Systems). County and health district rules routinely exceed them, code text changes, and only State Water Resources Control Board — OWTS Policy or your local health department can confirm what applies to your parcel.
Send your sizing numbers to installers who work under California rules every day.