Last checked: October 22, 2026

How a private well works

A household well is a hole that reaches groundwater, a pipe that keeps the hole open and sealed, a pump that lifts the water, and a pressure tank that keeps it flowing to your taps. Knowing the parts helps you spot problems and talk to a well contractor. Here's how each piece works, with sources.

Where the water comes from: the aquifer

Below the ground, the spaces between soil grains and the cracks in rock fill with water. USGS calls the top of that saturated zone the water table. Rock or sediment that holds water and readily gives it up to wells and springs is an aquifer. Precipitation eventually soaks down and recharges it, though not at the same rate everywhere.¹

Two things USGS points out that matter to well owners:

• Pumping draws the water level down. Pumping too much water too fast can make a well yield less and less water and even run dry, and heavy pumping can even cause a neighbor's well to run dry if you both draw from the same aquifer.¹
• Some aquifers are under pressure. In a confined ("pressurized") aquifer, the pressure may push water up the well, and sometimes right out of it, without a pump. USGS calls these artesian aquifers and artesian wells.¹

The three types of wells

EPA describes three types of private drinking water wells.²

A few more details from USGS:

• Dug wells lack continuous casing, which makes them subject to contamination from nearby surface sources, and they can go dry during droughts if the water table drops below the bottom of the well.³
• Driven wells are still common. They're built by driving a small-diameter pipe into soft earth such as sand or gravel, with a screen at the bottom.³
• Drilled wells are the type New York's health department recommends for a home, when properly located and built. It says well points, dug wells, springs and shore wells are more susceptible to drought and to contamination.⁴ The buying guide covers why inspectors flag dug wells.

Not sure which you have? The well log (construction report) records the depth, casing and geology. Many states have a searchable database; see your state page.

The parts of a well

EPA (adapting the National Ground Water Association) describes the basic parts:²

• Casing: the pipe that keeps the hole open from the groundwater up to the surface. With grout around it, the casing keeps out dirt, surface water and lower-quality groundwater. Carbon steel, plastic and stainless steel are the most common materials. Some states and local agencies set minimum casing lengths.
• Well cap: sits on top of the casing to keep out debris, insects and small animals. Usually aluminum or plastic, with a vent to control pressure while pumping.
• Well screen: attached to the bottom of the casing to keep too much sediment out.
• Pitless adapter: a fitting that lets the water line leave the casing below the frost line, keeping a sanitary, frost-proof seal.
• Pump: see below.

New York's health department says homeowners should inspect the casing, cap and area around the well at least once a year to make sure the well is protected from contamination, and replace an unacceptable cap.⁴ Minnesota requires the casing to stick up at least 12 inches above the ground.⁵

The pump

EPA says:²

• Jet pumps are the most common pumps for shallow wells (25 feet deep or less). They sit above ground and use suction to pull water up.
• Submersible pumps are the most common for deep wells. The pump sits down inside the casing and is wired to power at the surface.

Clemson Extension notes that groundwater has to be pumped up using a power source, usually electricity, and that a check valve keeps water from flowing back down into the well.⁶ New York's health department says submersible pumps need very little maintenance, while jet and suction pumps should be kept dry and may need priming now and then.⁴

The pressure tank and pressure switch

The pump doesn't run every time you open a tap. New York's health department describes the cycle:⁴

1. When you open a faucet, compressed air in the pressure tank pushes water out to the fixture.
2. As the tank empties, the pressure drops, and the pressure switch (on or near the tank) turns the pump on.
3. The pump refills the tank from the well. At a preset level, the switch turns the pump off.

Settings vary. Clemson gives an example of a switch that turns the pump on below 30 psi and off at 50 psi, and says a pressure gauge helps you check that the settings are right.⁶ New York's health department says switches typically keep the tank between 30 and 50 psi or 40 and 60 psi, and that they run on higher-than-normal household voltage, so call a well driller or electrician for switch work.⁴ University of Arizona Extension says the start-up setting is usually 20, 30 or 40 psi.⁷

Why the tank matters: New York's health department says the pressure tank maintains pressure in the household plumbing and keeps the pump from running every time water is needed, which lengthens pump life. Signs of a tank problem include the pump running more often than usual, surging water pressure, and taste and odor issues. It recommends calling a plumber or well driller if you suspect one.⁴

Some systems also have a separate storage tank. New York notes some well systems include one holding a few hundred gallons.⁴ Low-yield wells often need one; see flow and yield tests.

Where the well sits matters

EPA says a well should be located so rainwater flows away from it, because rainwater can pick up bacteria and chemicals and seep into a well if it pools nearby. Proper construction depends on local geology and groundwater, and EPA suggests your state well-contractor licensing agency or local health department for advice. It also recommends drillers and pump installers who are bonded and insured, and licensed and certified where your state requires it.² New York recommends storing pesticides, fertilizers, fuels and similar products at least 100 feet from the well casing.⁴

Related guides

• Why do so many U.S. households use private wells?
• Private well vs city water: pros, cons and costs
• Who regulates private wells?
• Shock chlorinating a well
• Well flooded? What to do
• How often should you test a private well?