Mississippi · 15 Miss. Code R. 18-77
Septic system requirements in Mississippi
Tank sizes, drainfield rules, setbacks, permits, and real costs — pulled from Mississippi's own code rather than a national average.
- 3-bedroom tank
- 1,000 gal
- Design flow
- 150 gpd/BR
- Typical install
- $5,000–$14,000
- Permit fee
- $100–$400
- Well setback
- 100 ft
- Permitted by
- State agency
Septic tank sizes required in Mississippi
Mississippi sizes systems on a design flow of 150 gallons per day per bedroom. 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 | 150 gpd | 1,000 gal | 1,000 gal |
| 2 bedrooms | 300 gpd | 1,000 gal | 1,000 gal |
| 3 bedrooms | 450 gpd | 1,000 gal | 1,000 gal |
| 4 bedrooms | 600 gpd | 1,000 gal | 1,250 gal |
| 5 bedrooms | 750 gpd | 1,250 gal | 1,500 gal |
| 6 bedrooms | 900 gpd | 1,500 gal | 2,000 gal |
Source: 15 Miss. Code R. 18-77. 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 Mississippi at 450 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 | 563 ft² | 1,126 ft² | $9,300 |
| Sandy loam | 0.5 gpd/ft² | 900 ft² | 1,800 ft² | $11,800 |
| Loam | 0.4 gpd/ft² | 1,125 ft² | 2,250 ft² | $13,500 |
| Silt loam | 0.3 gpd/ft² | 1,500 ft² | 3,000 ft² | $16,300 |
| Clay loam | 0.2 gpd/ft² | 2,250 ft² | 4,500 ft² | $21,900 |
Estimates use Mississippi's cost index of 0.83× the national average. Build a line-item estimate →
Permits and who issues them
The Mississippi State Department of Health runs the program statewide and licenses installers and site evaluators.
| Permit required | Yes |
|---|---|
| Typical fee | $100 – $400 |
| 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 | 5 ft |
| Surface water | 50 ft |
| Building foundation | 10 ft |
Regulatory contact
Mississippi State Department of Health — Onsite Wastewater
msdh.ms.gov · 601-576-7690
What makes septic hard in Mississippi
Delta counties sit on deep, essentially impermeable alluvial clay where conventional drainfields simply do not work — aerobic units with surface discharge dominate.
The Yazoo Basin has a water table within inches of the surface for much of the year.
Loess bluff soils east of the Delta are prone to severe erosion around disturbed ground.
Things that catch people out
- A 48-hour retention requirement applies on top of the bedroom table, so tanks are often larger than the table alone suggests.
- The drainfield-to-well setback is 100 feet but the tank-to-well setback is only 50 — designers get these backwards regularly.
Mississippi septic questions
What size septic tank do I need in Mississippi?
A three-bedroom home in Mississippi requires a minimum 1,000 gallon tank under 15 Miss. Code R. 18-77. Design flow is 150 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 Mississippi?
Yes. The Mississippi State Department of Health runs the program statewide and licenses installers and site evaluators. Fees typically run $100 to $400, 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 Mississippi?
A conventional system for a three-bedroom home typically runs $5,000 to $14,000 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 Mississippi 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.
- 15 Miss. Code R. 18-77 — Individual Onsite Wastewater Disposal Systems · verified 2026-09-18
- MSDH Design Standard Ch. 5 — Individual Onsite Wastewater Disposal Design Standard · verified 2026-09-18