Texas · 30 Texas Administrative Code Chapter 285
TCEQ writes Chapter 285 and delegates permitting to Authorized Agents — usually counties, sometimes cities or river authorities — which administer the program locally.
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.
Blackland Prairie clay running through Dallas, Waco, Austin and San Antonio with severe shrink-swell and very slow percolation. Caliche in central and west Texas. East Texas has sandy soils that percolate well. The Hill Country has thin soil over limestone.
Aerobic treatment units with surface spray irrigation are the dominant residential system across the Texas clay belt — a defining feature of the state. Conventional trenches remain common in east Texas sands. Low pressure dosing and drip irrigation are used in the Hill Country.
| Dwelling | Design flow | Minimum tank | With disposal |
|---|---|---|---|
| 1 bedroom | 300 gpd | 1,000 gal | 1,250 gal |
| 2 bedrooms | 300 gpd | 1,000 gal | 1,250 gal |
| 3 bedrooms | 450 gpd | 1,000 gal | 1,250 gal |
| 4 bedrooms | 600 gpd | 1,250 gal | 1,500 gal |
| 5 bedrooms | 750 gpd | 1,500 gal | 1,750 gal |
The Authorized Agent for your area issues the permit, and there are hundreds of them. Texas requires a site evaluation by a licensed professional — a Professional Sanitarian, Registered Sanitarian or Professional Engineer — and licenses installers in two classes. Aerobic systems require a maintenance contract for the first two years, and continuing maintenance thereafter.
The state sets a floor. These Texas counties are where the largest septic populations sit, and where local requirements most often exceed it.
| County | What makes it different |
|---|---|
| Harris | Houston; high water table and clay, extensive on-site use in unincorporated areas |
| Montgomery | Rapid growth north of Houston, sandy to clay transition |
| Bexar | San Antonio; Edwards Aquifer recharge zone imposes major restrictions |
| Travis | Austin area; Hill Country rock and aquifer protection |
| Collin | Blackland clay, heavy aerobic system use |
| Hays | Hill Country growth over the Edwards Aquifer |
| Denton | North Texas clay, rapid development |
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.
Aerobic units require a maintenance contract and periodic reporting to the Authorized Agent; conventional systems have no mandated interval. Use the pump schedule calculator to work out the interval for your tank size and household.
Regional labour and permit costs in Texas run about 94% of the national baseline. Here is what typical installations land at for a three-bedroom home:
| System type | Typical installed cost in Texas | When it applies |
|---|---|---|
| Conventional gravity | $8,500 – $15,000 | Good soil, adequate depth to water |
| Chamber system | $9,400 – $17,200 | Alternative to gravel trenches |
| Mound system | $16,200 – $31,500 | Shallow water table or thin soil |
| Aerobic treatment | $13,600 – $27,000 | Clay soil or small lots |
| Tank pump-out (service) | $300 – $610 | 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 30 Texas Administrative Code Chapter 285, On-Site Sewage Facilities. County and health district rules routinely exceed them, code text changes, and only Texas TCEQ — On-Site Sewage Facilities Program or your local health department can confirm what applies to your parcel.
Send your sizing numbers to installers who work under Texas rules every day.