Mississippi · Mississippi State Department of Health Regulation Governing Individual On-Site Wastewater Disposal Systems
The Mississippi State Department of Health administers the program directly, with district environmental health staff.
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.
Delta clay in the northwest with a shallow water table, loess bluffs along the Mississippi River, and sandy coastal plain in the south. Yazoo clay around Jackson is notoriously difficult, with severe shrink-swell behaviour.
Conventional trenches on the coastal plain sands. Through the Delta and Yazoo clay areas, aerobic treatment units and mechanical plants with surface discharge are common, similar to neighbouring Louisiana.
| 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 |
Mississippi licenses installers and requires a site evaluation by department staff or a certified evaluator. Aerobic units require ongoing maintenance arrangements.
The state sets a floor. These Mississippi counties are where the largest septic populations sit, and where local requirements most often exceed it.
| County | What makes it different |
|---|---|
| DeSoto | Memphis suburbs, fast growth |
| Rankin | Jackson metro; Yazoo clay |
| Madison | Suburban growth on difficult clay |
| Harrison | Gulf coast, sandy but high water table |
| Jackson County | Coastal, mixed conditions |
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 servicing under the maintenance provisions. Use the pump schedule calculator to work out the interval for your tank size and household.
Regional labour and permit costs in Mississippi run about 86% of the national baseline. Here is what typical installations land at for a three-bedroom home:
| System type | Typical installed cost in Mississippi | When it applies |
|---|---|---|
| Conventional gravity | $7,700 – $13,800 | Good soil, adequate depth to water |
| Chamber system | $8,500 – $15,900 | Alternative to gravel trenches |
| Mound system | $14,600 – $29,000 | Shallow water table or thin soil |
| Aerobic treatment | $12,300 – $24,800 | Clay soil or small lots |
| Tank pump-out (service) | $280 – $560 | 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 Mississippi State Department of Health Regulation Governing Individual On-Site Wastewater Disposal Systems. County and health district rules routinely exceed them, code text changes, and only Mississippi State DOH — Onsite Wastewater or your local health department can confirm what applies to your parcel.
Send your sizing numbers to installers who work under Mississippi rules every day.