Septic tank size by state / South Atlantic
Delaware septic tank size
In Delaware the minimum septic tank for a three-bedroom house is 1,000 gallons, and four bedrooms need the same 1,000 gallons. The figure comes from 7 Del. Admin. Code 7101 §5.3.14.4 (septic tanks) and §5.3.3.3 (design flow), which sizes the tank from design flow; the bedroom figures below are that rule's arithmetic. That matches the 1,000-gallon median of the 47 states listed here.
What the Delaware rule says
The rule is 7 Del. Admin. Code 7101 §5.3.14.4 (septic tanks) and §5.3.3.3 (design flow), administered by Delaware Department of Natural Resources and Environmental Control (DNREC), Division of Water, Groundwater Discharges Section. In its own words:
For flows <= 500 gpd the minimum liquid working capacity shall be 1,000 gallons. For flows > 500 gpd but < 2,500 gpd shall have a working capacity of 1.5 times the expected flow rate ... with a minimum liquid working capacity of 1,500 gallons.
Source: 7 Del. Admin. Code 7101 §5.3.14.4 (septic tanks) and §5.3.3.3 (design flow), read 2026-10-20.
- Delaware sizes the tank from design flow: 120 gallons a day per bedroom, at least 240 a day per home.
- Up to four bedrooms that works out to the 1,000-gallon minimum; five to eight bedrooms to 1,500 gallons.
- DNREC can require a larger tank where big flow surges are expected.
Delaware minimum tank size by bedrooms
| Bedrooms | Minimum tank | Versus the median state |
|---|---|---|
| 1 | 1,000 gal | same |
| 2 | 1,000 gal | — |
| 3 | 1,000 gal | same |
| 4 | 1,000 gal | −200 |
| 5 | 1,500 gal | same |
| 6 | 1,500 gal | — |
The first step up comes at 5 bedrooms, from 1,000 to 1,500 gallons, and a six-bedroom house needs 1,500 gallons. These are minimums: the permit can call for more, and a bigger tank needs pumping less often.
How Delaware compares with nearby states
Florida requires 900 gallons for three bedrooms; Georgia requires 1,000 gallons for three bedrooms; Maryland requires 1,000 gallons for three bedrooms; North Carolina requires 1,000 gallons for three bedrooms; South Carolina requires 1,000 gallons for three bedrooms; Virginia requires 900 gallons for three bedrooms; West Virginia requires 1,000 gallons for three bedrooms. 37 of the 47 states listed here share Delaware's three-bedroom figure.
Before you size a tank in Delaware
- 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 Delaware'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.