Septic tank size by state / West North Central
Iowa septic tank size
In Iowa the minimum septic tank for a three-bedroom house is 1,250 gallons, rising to 1,500 gallons at four bedrooms. The figure comes from Iowa Admin. Code 567—69.3(2)(a), Table I (as renumbered by ARC 9467C, eff. 9/10/25). That is 250 gallons more than the 1,000-gallon median of the 47 states listed here.
What the Iowa rule says
The rule is Iowa Admin. Code 567—69.3(2)(a), Table I (as renumbered by ARC 9467C, eff. 9/10/25); design flow 567—69.1(9)(a), administered by Iowa Department of Natural Resources (Environmental Protection Commission); permits by county boards of health. In its own words:
Up to and including 3-bedroom homes 1,250 gal. 4-bedroom homes 1,500 gal. 5-bedroom homes 1,750 gal. 6-bedroom homes 2,000 gal. Each additional bedroom + 250 gal.
Source: Iowa Admin. Code 567—69.3(2)(a), Table I (as renumbered by ARC 9467C, eff. 9/10/25), read 2026-10-20.
- Iowa's floor is unusually high: 1,250 gallons even for one to three bedrooms.
- Design flow is 150 gallons per bedroom per day. The rule was renumbered to 567—69.3 in September 2025.
Iowa minimum tank size by bedrooms
| Bedrooms | Minimum tank | Versus the median state |
|---|---|---|
| 1 | 1,250 gal | +250 |
| 2 | 1,250 gal | — |
| 3 | 1,250 gal | +250 |
| 4 | 1,500 gal | +300 |
| 5 | 1,750 gal | +250 |
| 6 | 2,000 gal | — |
The first step up comes at 4 bedrooms, from 1,250 to 1,500 gallons, and a six-bedroom house needs 2,000 gallons. Beyond the table the rule adds 250 gallons for each extra bedroom. These are minimums: the permit can call for more, and a bigger tank needs pumping less often.
How Iowa compares with nearby states
Kansas requires 1,000 gallons for three bedrooms; Minnesota requires 1,000 gallons for three bedrooms; Missouri requires 1,000 gallons for three bedrooms; Nebraska requires 1,000 gallons for three bedrooms; North Dakota requires 1,000 gallons for three bedrooms; South Dakota requires 1,000 gallons for three bedrooms. 1 of the 47 states listed here share Iowa's three-bedroom figure.
Before you size a tank in Iowa
- Bedrooms, not people, set the size in most rules. Rooms that could be used as bedrooms are usually counted, so check how your permitting office counts a den or a finished basement.
- Garbage disposals, grinder or ejector pumps and large tubs change the answer in many states; the points above list Iowa's adjustments.
- The tank is only half the system. The drainfield is sized separately from soil tests, and it is usually the bigger cost.
- A private well on the same lot has its own setbacks from the tank and field; the well pump and pressure tank calculators size the water side.
Figures are the state's minimum as written on 2026-10-20. Local health departments can require more; the permit issued for your property governs. See the methodology for how each state was read.