Arizona · A.A.C. R18-9-A314
Septic system requirements in Arizona
Tank sizes, drainfield rules, setbacks, permits, and real costs — pulled from Arizona's own code rather than a national average.
- 3-bedroom tank
- 1,000 gal
- Design flow
- 150 gpd/BR
- Typical install
- $7,000–$19,000
- Permit fee
- $300–$1,200
- Well setback
- 100 ft
- Permitted by
- County / local
Septic tank sizes required in Arizona
Arizona sizes systems on a design flow of 150 gallons per day per bedroom. The tank must meet both the bedroom table below and a 2.1× 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 | 1,250 gal | 1,500 gal |
| 5 bedrooms | 750 gpd | 1,500 gal | 2,000 gal |
| 6 bedrooms | 900 gpd | 1,750 gal | 2,000 gal |
Source: A.A.C. R18-9-A314. 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 Arizona 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 | $10,900 |
| Sandy loam | 0.5 gpd/ft² | 900 ft² | 1,800 ft² | $13,800 |
| Loam | 0.4 gpd/ft² | 1,125 ft² | 2,250 ft² | $15,600 |
| Silt loam | 0.3 gpd/ft² | 1,500 ft² | 3,000 ft² | $18,800 |
| Clay loam | 0.2 gpd/ft² | 2,250 ft² | 4,500 ft² | $25,100 |
Estimates use Arizona's cost index of 0.93× the national average. Build a line-item estimate →
Permits and who issues them
ADEQ writes the rules and has delegated permitting to county environmental health departments in most of the state, including Maricopa and Pima.
| Permit required | Yes |
|---|---|
| Typical fee | $300 – $1,200 |
| Soil evaluation | Required before permit |
| Licensed installer | Required |
| Turnaround | 2–6 weeks |
| Ongoing inspection | Transfer-of-ownership inspection required within 6 months before conveyance |
| 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 |
|---|---|
| Property line | 5 ft |
| Surface water | 50 ft |
| Building foundation | 5 ft |
Regulatory contact
Arizona Department of Environmental Quality — Onsite Wastewater
www.azdeq.gov · 602-771-2300
What makes septic hard in Arizona
Caliche — a cemented calcium-carbonate hardpan — sits close to the surface across much of central and southern Arizona. It has to be broken out, and it turns a routine excavation into a rock job.
Shallow bedrock in the high country around Prescott, Payson, and Flagstaff frequently fails the vertical-separation requirement.
Monsoon flooding means designs have to account for sudden saturation of a normally bone-dry site.
Things that catch people out
- Arizona requires a transfer-of-ownership inspection before a property with an on-site system changes hands. Budget for it, and do not assume the seller has one.
- The design capacity is 2.1 times daily design flow for anything that is not a single-family dwelling, which catches guest houses and casitas.
Arizona septic questions
What size septic tank do I need in Arizona?
A three-bedroom home in Arizona requires a minimum 1,000 gallon tank under A.A.C. R18-9-A314. Design flow is 150 gallons per day per bedroom, and the tank must also hold 2.1 times daily flow, so the practical recommendation is 1,000 gallons.
Do I need a permit for a septic system in Arizona?
Yes. ADEQ writes the rules and has delegated permitting to county environmental health departments in most of the state, including Maricopa and Pima. Fees typically run $300 to $1,200, with a turnaround of about 2–6 weeks. A soil evaluation or percolation test is required before a permit is issued.
How much does a septic system cost in Arizona?
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 Arizona drainfield be from a well?
100 feet from a private water well. Local rules can be stricter.
Sources
Every figure on this page traces to one of these documents.
- A.A.C. R18-9-A314 — Septic tank design, manufacturing, and installation · verified 2026-09-18
- A.A.C. R18-9-E302 — 4.02 General Permit: Septic Tank with Disposal Works · verified 2026-09-18