New York · 10 NYCRR Appendix 75-A
The New York State Department of Health writes Appendix 75-A; county health departments administer it, and several counties impose considerably stricter requirements.
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.
Enormous variation. Long Island sits on sandy outwash over a sole source aquifer. The Hudson valley has clay and shale. The Adirondacks and Catskills have thin soil over rock. Western New York has heavy lake plain clay.
Conventional absorption trenches, fill systems and raised systems on tight soil. On Long Island, nitrogen-reducing innovative/alternative systems are now required for new construction in Suffolk County — one of the most consequential local rules in the 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 New York City watershed counties operate under watershed rules that are stricter than 75-A, and Suffolk County's Article 6 requirements for nitrogen reduction apply to new and replacement systems. Both override the state baseline substantially.
The state sets a floor. These New York counties are where the largest septic populations sit, and where local requirements most often exceed it.
| County | What makes it different |
|---|---|
| Suffolk | Long Island; I/A nitrogen-reducing systems required, sole source aquifer |
| Nassau | Largely sewered, remaining on-site systems face nitrogen rules |
| Dutchess | Hudson valley; clay soils and watershed proximity |
| Orange | Growth corridor with mixed soils |
| Ulster | NYC watershed rules apply in part |
| Westchester | Watershed regulations and small lots |
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.
Suffolk County requires maintenance contracts on I/A systems; watershed counties impose inspection obligations. Use the pump schedule calculator to work out the interval for your tank size and household.
Regional labour and permit costs in New York run about 134% of the national baseline. Here is what typical installations land at for a three-bedroom home:
| System type | Typical installed cost in New York | When it applies |
|---|---|---|
| Conventional gravity | $12,100 – $21,400 | Good soil, adequate depth to water |
| Chamber system | $13,300 – $24,600 | Alternative to gravel trenches |
| Mound system | $23,000 – $44,900 | Shallow water table or thin soil |
| Aerobic treatment | $19,400 – $38,500 | Clay soil or small lots |
| Tank pump-out (service) | $430 – $870 | 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 10 NYCRR Appendix 75-A, Wastewater Treatment Standards for Residential Onsite Systems. County and health district rules routinely exceed them, code text changes, and only New York State DOH — Residential Onsite Systems or your local health department can confirm what applies to your parcel.
Send your sizing numbers to installers who work under New York rules every day.