Short definition
A drilled well is the standard modern private well: a rotary or percussion rig advances steel or PVC casing into the ground, the borehole continues into a producing aquifer, a screen at the bottom admits water, and a submersible pump lifts it to a pressure tank in the house. Depths typically run 50 to 600 feet, depending on where the aquifer sits.
What it is
Construction follows a standard sequence: a licensed driller bores into the ground, sets casing as the hole advances, seals the gap between the casing and the surrounding soil with bentonite or grout, places a well screen in the producing zone, drops in a submersible pump on a length of pipe, wires the pump up to a pressure switch on the surface, and connects everything to a pressure tank. A pitless adapter lets the supply line exit the casing below the frost line without breaking the seal.
Drilled wells dominate modern Washington well construction. They handle hard rock and deep aquifers — the conditions that defeat older driven and dug wells — and they isolate the wellhead from surface contamination far better than legacy designs.
Why it matters to a homeowner
If you’re buying or already own a rural Washington property, the drilled well is almost certainly what you have. Practical implications:
- Yield and depth set the price. Drillers quote per foot. Aquifer depth, rock conditions, and casing requirements all move the number.
- The pump is the failure point. Submersible pumps last 8 to 15 years; replacement requires hoisting the pump and drop pipe out of the casing, which is a service call, not a DIY job.
- The seal is the contamination point. A failed grout seal, corroded casing, or cracked cap can let surface water reach the aquifer — the most common cause of a positive coliform test on an annual sample.
- Annexation changes the math. If your area annexes into a city water system, you can connect to municipal water and decommission the well, but decommissioning is a regulated process under Washington’s well code.
Washington note
Washington wells are constructed under WAC 173-160 (the Department of Ecology’s well construction standards) by drillers licensed under RCW 18.104. A few rules that show up on inspections and well logs:
- Casing extends at least 6 inches above grade, and at least 2 feet above the 100-year flood elevation if the well is in a flood plain. Source: WAC 173-160-291.
- Pitless adapters are permitted with approved fittings, generally above static water level (limited exceptions exist for designs intended for below-static use).
- A well log (well construction report) is filed with Ecology by the driller after construction. Homeowners can request a copy from Ecology’s well log database — useful when buying a property, replacing a pump, or troubleshooting yield.
For decommissioning, sealing rules under WAC 173-160 Part 2 apply; you cannot simply abandon an old well in place.
Common failure modes
- Casing corrosion in older steel-cased wells — opens contamination paths from the surface.
- Pitless adapter O-ring failure — leak between casing and supply line; loss of pump prime.
- Submersible pump failure in deep installations — costly hoist-out and replacement.
- Yield decline from aquifer drawdown over decades, especially as nearby wells multiply.
- Cap or seal failure — shows up as positive coliform on an annual water test.