Missouri · 19 CSR 20-3.060
The Missouri Department of Health and Senior Services sets the standard, but counties that have adopted their own ordinance administer it locally, and many have.
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.
Ozark karst across the south with thin soil over limestone and abundant sinkholes and springs. Northern Missouri has glacial till with claypan. River bottoms are alluvial.
Conventional trenches where soil depth allows. Lagoons remain permitted in parts of rural Missouri. Low-pressure pipe and drip distribution are used on thin Ozark soils.
| 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 |
Missouri requires soil morphology evaluation by a registered onsite soil evaluator for most designs, and registers installers. County ordinances layer additional requirements in many jurisdictions.
The state sets a floor. These Missouri counties are where the largest septic populations sit, and where local requirements most often exceed it.
| County | What makes it different |
|---|---|
| St. Charles | Rapid suburban growth |
| Jefferson | Large septic population south of St. Louis |
| Greene | Springfield; Ozark karst |
| Christian | Fast-growing karst county |
| Camden | Lake of the Ozarks; strict shoreline requirements |
| Franklin | Rural growth on mixed soils |
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.
Set by county ordinance where adopted. Use the pump schedule calculator to work out the interval for your tank size and household.
Regional labour and permit costs in Missouri run about 90% of the national baseline. Here is what typical installations land at for a three-bedroom home:
| System type | Typical installed cost in Missouri | When it applies |
|---|---|---|
| Conventional gravity | $8,100 – $14,400 | Good soil, adequate depth to water |
| Chamber system | $8,900 – $16,600 | Alternative to gravel trenches |
| Mound system | $15,400 – $30,200 | Shallow water table or thin soil |
| Aerobic treatment | $13,000 – $25,900 | Clay soil or small lots |
| Tank pump-out (service) | $290 – $580 | 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 19 CSR 20-3.060, Minimum Construction Standards for On-Site Sewage Systems. County and health district rules routinely exceed them, code text changes, and only Missouri DHSS — Onsite Sewage Program or your local health department can confirm what applies to your parcel.
Send your sizing numbers to installers who work under Missouri rules every day.