Well Caps: Types and Replacement
Water well caps sit on top of the casing and keep out debris, insects and small animals, and EPA notes most are aluminum or plastic with a vent to control pressure during pumping. A good one seals to the casing with a gasket and has a screened vent pointing down. EPA Region 8 says caps held by side set screws with no gasket shouldn't be used.
Swapping a cap on a standard casing is a bolt-on job most owners can handle with the power off. The catch is what you find when the old one comes off.
Types of well caps
| Cap type | How it seals | Notes |
|---|---|---|
| Old-style set-screw cap | Screws bite the casing, no gasket | EPA Region 8 says not to use these |
| Vermin-proof (sanitary) cap | Compression gasket around the casing, screened vent | Minnesota's wellhead guidance for noncommunity public systems recommends replacing older caps with an overlapping cap like this |
| Sanitary well seal | Plate fits inside the casing with a compression seal | An alternative to an overlapping cap, common in well houses |
| Locking cap | Same as a sanitary cap, with a lock or tamper bolts | Useful where the well is near a road or shared lot |
Most homes want the vermin-proof cap. It costs a bit more than the old style, and it's the one that keeps the critters out.
What codes expect
Rules come from your state or county health department, so check locally. Two published examples give you the idea:
- Casing height. Minnesota's wellhead rules for noncommunity public water systems require the casing to stand at least 12 inches above the ground. EPA Region 8 calls for 12 inches above the floor indoors and 18 inches above the natural ground outdoors.
- Sealing. Region 8 calls for a watertight neoprene gasket, and says caulk is not an acceptable fix for any opening on a well.
- Vent. It must face down and be covered with #24 mesh non-corrodible screen.
- Wiring. Those same Minnesota rules require exposed wiring above grade to be in electrical conduit.
If your cap is at ground level or buried, the cap isn't the real problem. The casing needs an extension, and that's a well contractor's job.
Signs your cap needs replacing
- Cracks, a missing bolt, or a gasket that's torn or flattened
- Bugs, spider webs or mouse droppings inside the cap
- A vent screen that's missing or rusted through
- Mower damage or a cap that rocks on the casing
- Bacteria showing up in your water test after a clean history
EPA tells well owners to look periodically for a broken or missing cap, cracked or corroded casing, and settling around the well. Take a look every spring.
Tools and parts
- New cap sized to your casing's outside diameter. Household casing is typically 4 to 6 inches. Measure it; don't guess.
- Socket or nut driver for the cap bolts
- Clean rag and a stiff brush
- Chlorine for disinfecting afterward
How to replace a well cap
Power off
Shut off the pump breaker, and confirm the pump won't run.
Remove the old cap
Loosen the bolts or screws and lift the cap straight up. Watch the wire, which may come through the cap.
Look down the casing
Use a flashlight. Note debris, insects or a damaged casing top. Remove anything you can reach safely.
Clean the casing rim
Wipe off dirt and old gasket material so the new gasket can seat.
Fit the new cap
Slide it over the casing with the gasket in place. Route the pump wire through the cap's conduit fitting or grommet, as EPA Region 8 recommends for submersible wire openings.
Tighten the bolts evenly
Work around the cap so the gasket compresses all the way around. Check that the vent points down.
Disinfect the well
Minnesota's handbook says to disinfect the well whenever it's opened for repairs. Our shock chlorination guide walks through it.
Test the water
EPA says to test after any repair to the well system.
Mistakes to avoid
- Sealing the vent shut. The well needs to breathe as the water level moves.
- Using caulk or tape. Region 8 says caulk is not acceptable on any well opening. Replace the gasket.
- Burying the casing. EPA warns never to cut the casing below the land surface. Keep the ground sloped away from the well and don't pile mulch or snow on it.
- Mismatched size. A cap that's "close enough" won't seal.
When it's a pro job
Call a licensed well contractor when water is coming out of the cap, when the casing is cracked, too short or buried, or when the pump wire is damaged. Water flowing out of the top usually means a flowing (artesian) well or a pressure problem, and both need a contractor. For casing damage, see well casing problems.
HomeGuide puts a well cap and seal replacement at $300 to $500 with parts and labor.
FAQ
How do you remove a well cap?
Turn off the pump power, loosen the bolts or set screws around the side, and lift the cap straight up. Go slowly, because the pump wire may be attached to the cap. If it's stuck, a little penetrating oil on the bolts helps; don't pry against the casing.
Are well caps sealed?
A sanitary or vermin-proof cap is, with a gasket around the casing and a screened vent. Old set-screw caps aren't, which is why Region 8 says not to use them.
How do I find a buried well cap?
Look for a slight dip or a patch of different grass near the house, follow the water line from the basement, and check the old well record. Then have the casing extended above grade. A buried cap lets surface water down the well.
What does a capped well look like?
On most homes, a round aluminum or plastic cap on a steel or plastic pipe sticking up out of the ground. You'll often see a conduit for the pump wire coming out of it.
Why is water coming out of my well cap?
It can be a flowing artesian well, a flooded area, or water backing up from a pressure problem. Shut off the pump and call a well contractor rather than sealing it shut.
Sources
- U.S. EPALearn About Private Water Wells (opens in a new tab)
- U.S. EPA Region 8 Drinking Water UnitTech Tips: Simple Fixes for Wellheads (opens in a new tab)
- Minnesota Department of HealthNoncommunity Public Water System Wellhead Requirements (opens in a new tab)
- U.S. EPAProtect Your Home's Water (opens in a new tab)
- Minnesota Department of HealthWell Owner's Handbook: A Consumer's Guide to Water Wells in Minnesota (opens in a new tab)
- HomeGuideHow Much Does Well Pump Repair Cost? (opens in a new tab)