How a Well System Works

Where does the water come from?

Well water comes from groundwater, which is water held in the spaces of soil, sand, gravel or fractured rock below the surface. The layer that holds enough water to supply a well is called an aquifer. Some aquifers are shallow and respond quickly to rain and drought. Others are deeper and change slowly.

Depth, rock type and nearby land use all shape how much water your well gives and what is dissolved in it. That is why two neighbors can have very different water. Your state geological survey or county health office can tell you what is typical locally.

What does the well casing do?

The casing is the pipe that lines the upper part of the borehole. Its job is to keep the hole from collapsing and to keep surface water and shallow groundwater from running straight down into the drinking supply. A sealed space around the casing, set when the well is built, adds more protection.

At the top, a well cap or sanitary seal closes the casing. A cracked cap, missing seal or casing that has been damaged by equipment can let in insects, animals and runoff. Looking at the wellhead a couple of times a year is cheap protection.

• Casing: lines the hole and blocks surface water
• Seal and cap: close the top of the well
• Screen or open bottom: where water enters, depending on well type

How does the pump move water?

Most modern household wells use a submersible pump that sits down in the water and pushes it up through a pipe. Older or shallow systems may use a jet pump at the house that pulls water up. Both do the same job: create enough pressure to bring the water to the surface and into your plumbing.

A pump is an electric motor in a wet, hard to reach place. It works hard and will eventually wear out. Wiring, a control box and a pressure switch all affect whether it runs properly, so a pump that will not start does not always mean the pump itself has failed.

If the pump runs and no water comes out, or the water suddenly turns cloudy, a licensed professional should check the well rather than the homeowner experimenting with the equipment.

What does the pressure tank do?

The pressure tank holds a reserve of water under pressure. When you open a tap, the tank supplies water first, and the pump only starts once the pressure falls to a set point. Without a tank, the pump would turn on and off every time you ran water for a few seconds, which wears the motor out quickly.

A pressure switch near the tank senses the pressure and turns the pump on and off. A gauge shows what the system is doing. If the pump cycles rapidly, the tank or its air charge may be the cause. A licensed pump professional should diagnose it, since tanks hold stored pressure and can be dangerous to open.

How does water reach the house, and where does treatment fit?

From the tank, water travels through the main line to the house. Along the way it may pass a sediment filter, a softener, an iron filter, an ultraviolet unit or another treatment device, depending on what a lab test has shown. Treatment is added only for a specific problem found in testing, not as a general precaution.

Buried lines can freeze, leak or be cut during digging. Know the route of your water line and keep a simple sketch. It helps every contractor who works on the property later.

How can I keep the system running well?

Pay attention to normal. Notice how your pressure feels, how often the pump runs and what your water looks like. Small changes are the earliest signal that something needs checking, and a repair done early is nearly always cheaper than one done after a failure.

Keep records of tests, repairs and the name of whoever worked on the system. Ask a licensed professional to check the pump, tank and electrical parts when you move in or when behavior changes.

• Look at the wellhead each season
• Write down repair dates and who did the work
• Test water on the schedule your health department advises

What should I never do around a well?

Never pour chemicals, fuel or used oil near the wellhead, and never cut or cover the casing without professional advice. Do not open a pressure tank or work on wiring unless you are qualified, because stored pressure and electricity are both dangerous.

Avoid backfilling around the well with soil that traps water against the casing, and keep the area clear so a contractor can reach it. If you plan to build, dig or install fencing nearby, mark the wellhead and tell the crew where it is. Well damage from ordinary farm and yard equipment is more common than people think, and it can open a path for contamination.

If you ever suspect damage, stop using the water for drinking until a licensed professional and your county health office have advised you.

Last reviewed: November 12, 2026. Written by the Rural Farm Life Editorial Team. See our editorial policy.