Missouri · 19 CSR 20-3.060
Septic system requirements in Missouri
Tank sizes, drainfield rules, setbacks, permits, and real costs — pulled from Missouri's own code rather than a national average.
- 3-bedroom tank
- 1,000 gal
- Design flow
- 120 gpd/BR
- Typical install
- $7,000–$19,000
- Permit fee
- $150–$600
- Well setback
- 100 ft
- Permitted by
- State + local
Septic tank sizes required in Missouri
Missouri sizes systems on a design flow of 120 gallons per day per bedroom, with every dwelling rated for at least 2 bedrooms. The tank must meet both the bedroom table below and a 2× daily-flow detention requirement — whichever produces the larger number governs.
| Bedrooms | Design flow | Code minimum | Recommended |
|---|---|---|---|
| 1 bedroom | 240 gpd | 1,000 gal | 1,000 gal |
| 2 bedrooms | 240 gpd | 1,000 gal | 1,000 gal |
| 3 bedrooms | 360 gpd | 1,000 gal | 1,000 gal |
| 4 bedrooms | 480 gpd | 1,250 gal | 1,250 gal |
| 5 bedrooms | 600 gpd | 1,500 gal | 1,500 gal |
| 6 bedrooms | 720 gpd | 1,750 gal | 2,000 gal |
Source: 19 CSR 20-3.060. The recommended column rounds the governing requirement up to a tank size manufacturers actually stock.Run your own numbers →
Drainfield size and cost by soil type
For a three-bedroom home in Missouri at 360 gpd. This single table explains most of the variation between quotes — the area scales inversely with how fast your soil accepts water, and the drainfield is the largest line item in the job.
| Soil | Loading rate | Absorption area | With reserve | Typical total install |
|---|---|---|---|---|
| Medium sand | 0.8 gpd/ft² | 450 ft² | 900 ft² | $9,800 |
| Sandy loam | 0.5 gpd/ft² | 720 ft² | 1,440 ft² | $12,100 |
| Loam | 0.4 gpd/ft² | 900 ft² | 1,800 ft² | $13,600 |
| Silt loam | 0.3 gpd/ft² | 1,200 ft² | 2,400 ft² | $16,200 |
| Clay loam | 0.2 gpd/ft² | 1,800 ft² | 3,600 ft² | $21,300 |
Estimates use Missouri's cost index of 0.95× the national average. Build a line-item estimate →
Permits and who issues them
DHSS permits systems where the county has not adopted its own ordinance; many counties have, and those local rules then govern.
| Permit required | Yes |
|---|---|
| Typical fee | $150 – $600 |
| Soil evaluation | Required before permit |
| Licensed installer | Required |
| Turnaround | 2–5 weeks |
| Ongoing inspection | Not mandated statewide |
| Reserve area | 100% replacement area required |
Minimum setback distances
Measured horizontally from the drainfield unless noted. Local rules are frequently stricter, and on a small lot these numbers — not the soil — often decide the layout.
| Private water well | 100 ft |
|---|---|
| Well (septic tank) | 50 ft |
| Property line | 10 ft |
| Surface water | 50 ft |
| Building foundation | 10 ft |
Regulatory contact
Missouri Department of Health and Senior Services — Onsite Wastewater
health.mo.gov · 573-751-6095
What makes septic hard in Missouri
The Ozark plateau is karst over thin, rocky soil — fast pathways to groundwater and very little treatment capacity.
Northern Missouri claypan soils have some of the slowest percolation rates in the Midwest.
Whether the county or the state permits your system changes the rules and the fee, and there is no single list that is always current.
Things that catch people out
- Check first whether your county has adopted its own ordinance. If it has, the state rule is not what applies to you.
- The design flow floor is 240 gpd, so even a one-bedroom cabin is sized as a two-bedroom.
Missouri septic questions
What size septic tank do I need in Missouri?
A three-bedroom home in Missouri requires a minimum 1,000 gallon tank under 19 CSR 20-3.060. Design flow is 120 gallons per day per bedroom, and the tank must also hold 2 times daily flow, so the practical recommendation is 1,000 gallons.
Do I need a permit for a septic system in Missouri?
Yes. DHSS permits systems where the county has not adopted its own ordinance; many counties have, and those local rules then govern. Fees typically run $150 to $600, with a turnaround of about 2–5 weeks. A soil evaluation or percolation test is required before a permit is issued.
How much does a septic system cost in Missouri?
A conventional system for a three-bedroom home typically runs $7,000 to $19,000 installed. Soil quality moves this more than anything else — on tight clay requiring a mound, budget two to three times the low end.
How far must a Missouri drainfield be from a well?
100 feet from a private water well, with the septic tank itself allowed at 50 feet. Local rules can be stricter.
Sources
Every figure on this page traces to one of these documents.
- 19 CSR 20-3.060 — Minimum Construction Standards for On-Site Sewage Disposal Systems · verified 2026-09-18
- 19 CSR 20-3.060 — Missouri Secretary of State rule text · verified 2026-09-18