Short definition
A pitless adapter is a sealed brass fitting installed through the side wall of a well casing, below the local frost line. It lets the buried supply line exit the casing horizontally toward the house while the casing continues straight up to a sanitary cap above grade. It replaced the older “well pit” — a below-grade vault that historically housed the connection but invited contamination.
What it is
The fitting is a tee-shaped brass body bolted through a hole cut in the casing wall, with O-ring seals on the casing side. Inside the casing, a removable spool engages the drop pipe and pump cable. Outside the casing, a horizontal port connects to the supply line running below the frost line back to the house pressure tank.
The clever part is the spool. When a pump or drop pipe needs service, you lift the spool straight up out of the casing — bringing the pump and pipe with it — without disturbing the supply-line connection on the outside. That makes pump replacement a relatively contained job rather than the mess of an old well-pit setup.
Why it matters to a homeowner
Mostly, you’ll encounter pitless adapters during well rehabilitation, pump replacement, or a real-estate inspection on a rural Washington property. An inspector will confirm the well has a pitless adapter (and not a legacy well pit), because pits are a common code-deficiency finding on older installations.
When a quote says “retrofit pitless adapter” or “decommission existing well pit,” they’re modernizing the well-head connection to current Washington standards.
Washington note
Washington wells are constructed under WAC 173-160, the Department of Ecology’s well construction rules. WAC 173-160-291 addresses the upper terminal of the well: pitless adapters are permitted with department-approved fittings, generally above the static water level (with limited exceptions for designs intended for below-static use). The same section requires:
- The casing to extend at least 6 inches above grade.
- At least 2 feet above 100-year flood elevation in flood-prone sites.
- A mechanically secured or welded sanitary cap on top.
Pitless adapter installation is regulated trade work — wells are constructed by drillers licensed under RCW 18.104.
Common failure modes
- O-ring seal degradation over decades — pressure loss, possible contaminant ingress.
- Galvanic corrosion at the brass-to-steel-casing interface.
- Improper hole prep in the casing wall — won’t seal long-term.
- Frost heave shifting alignment in unusually deep cold installations.