Hawaii · H.A.R. Chapter 11-62
Septic system requirements in Hawaii
Tank sizes, drainfield rules, setbacks, permits, and real costs — pulled from Hawaii's own code rather than a national average.
- 3-bedroom tank
- 1,000 gal
- Design flow
- 75 gpd/BR
- Typical install
- $18,000–$48,000
- Permit fee
- $300–$1,200
- Well setback
- 50 ft
- Permitted by
- State agency
Septic tank sizes required in Hawaii
Hawaii sizes systems on a design flow of 75 gallons per day per bedroom, with every dwelling rated for at least 2 bedrooms. 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 | 150 gpd | 1,000 gal | 1,000 gal |
| 3 bedrooms | 225 gpd | 1,000 gal | 1,000 gal |
| 4 bedrooms | 300 gpd | 1,000 gal | 1,000 gal |
| 5 bedrooms | 375 gpd | 1,250 gal | 1,250 gal |
| 6 bedrooms | 450 gpd | 1,500 gal | 1,500 gal |
Source: H.A.R. Chapter 11-62. 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 Hawaii at 225 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 | 282 ft² | 564 ft² | $12,100 |
| Sandy loam | 0.5 gpd/ft² | 450 ft² | 900 ft² | $14,100 |
| Loam | 0.4 gpd/ft² | 563 ft² | 1,126 ft² | $15,500 |
| Silt loam | 0.3 gpd/ft² | 750 ft² | 1,500 ft² | $17,800 |
| Clay loam | 0.2 gpd/ft² | 1,125 ft² | 2,250 ft² | $22,300 |
Estimates use Hawaii's cost index of 1.35× the national average. Build a line-item estimate →
Permits and who issues them
The Department of Health Wastewater Branch permits every individual wastewater system in the state; there is no county-level delegation.
| Permit required | Yes |
|---|---|
| Typical fee | $300 – $1,200 |
| Soil evaluation | Required before permit |
| Licensed installer | Required |
| Turnaround | 6–16 weeks |
| Ongoing inspection | Required for aerobic units and NSF-certified treatment systems |
| 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 | 50 ft |
|---|---|
| Property line | 10 ft |
| Surface water | 100 ft |
| Building foundation | 5 ft |
Regulatory contact
Hawaii Department of Health — Wastewater Branch
health.hawaii.gov · 808-586-4294
What makes septic hard in Hawaii
Act 125 banned new cesspools in 2017 and requires the roughly 83,000 existing ones to be converted by 2050. That conversion mandate, not new construction, is the dominant septic issue in the state.
Young volcanic rock — especially a'a lava — offers almost no soil to treat effluent and is brutally expensive to excavate.
Every tank and component is shipped in, so materials carry ocean-freight pricing.
Shoreline setbacks and sea-level-rise exposure areas restrict siting on the most built-up coastlines.
Things that catch people out
- Hawaii uses 75 gpd per bedroom, the lowest design flow in the country, which makes tanks look small relative to the mainland — the constraint here is soil, not flow.
- If your property still has a cesspool, you are on a conversion clock with a hard 2050 deadline and a tax credit that does not cover the full cost.
Hawaii septic questions
What size septic tank do I need in Hawaii?
A three-bedroom home in Hawaii requires a minimum 1,000 gallon tank under H.A.R. Chapter 11-62. Design flow is 75 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 Hawaii?
Yes. The Department of Health Wastewater Branch permits every individual wastewater system in the state; there is no county-level delegation. Fees typically run $300 to $1,200, with a turnaround of about 6–16 weeks. A soil evaluation or percolation test is required before a permit is issued.
How much does a septic system cost in Hawaii?
A conventional system for a three-bedroom home typically runs $18,000 to $48,000 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 Hawaii drainfield be from a well?
50 feet from a private water well. Local rules can be stricter.
Sources
Every figure on this page traces to one of these documents.
- H.A.R. Chapter 11-62 — Wastewater Systems · verified 2026-09-18
- H.A.R. §11-62-31.1 — General requirements for individual wastewater systems · verified 2026-09-18