Arizona · Arizona Administrative Code Title 18
Arizona DEQ writes the rules and delegates permitting to county environmental health departments, which handle almost all residential work.
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.
Caliche is the defining problem — a cemented calcium carbonate layer that can be near-impenetrable and is common across central and southern Arizona. Elsewhere the state ranges from fast desert sands to tight clays, with shallow bedrock in the high country.
Conventional trenches and chambers where soil allows. Where caliche or rock intervenes, designs move to alternative systems from Arizona's approved general permit list, which is more structured than most states'.
| 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 |
Arizona uses a general permit system. Conventional systems fall under one general permit type, alternative technologies under others, and the applicable permit determines the design standard. A site investigation including soil profile and percolation testing is required.
The state sets a floor. These Arizona counties are where the largest septic populations sit, and where local requirements most often exceed it.
| County | What makes it different |
|---|---|
| Maricopa | Phoenix metro; large septic population on the fringes, caliche common |
| Pima | Tucson area; desert soils, variable caliche depth |
| Yavapai | Prescott area; shallow granite bedrock is the recurring obstacle |
| Pinal | Rapid growth on former agricultural land |
| Coconino | Flagstaff; volcanic rock, cinders, and a real freeze depth |
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.
Arizona requires an inspection and report at property transfer for on-site systems, which is stricter than most states. Use the pump schedule calculator to work out the interval for your tank size and household.
Regional labour and permit costs in Arizona run about 100% of the national baseline. Here is what typical installations land at for a three-bedroom home:
| System type | Typical installed cost in Arizona | When it applies |
|---|---|---|
| Conventional gravity | $9,000 – $16,000 | Good soil, adequate depth to water |
| Chamber system | $9,900 – $18,400 | Alternative to gravel trenches |
| Mound system | $17,100 – $33,600 | Shallow water table or thin soil |
| Aerobic treatment | $14,400 – $28,800 | Clay soil or small lots |
| Tank pump-out (service) | $320 – $650 | 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 Arizona Administrative Code Title 18, Chapter 9, Articles 1 through 3. County and health district rules routinely exceed them, code text changes, and only Arizona DEQ — On-site Wastewater Program or your local health department can confirm what applies to your parcel.
Send your sizing numbers to installers who work under Arizona rules every day.