What a submersible well pump does and where it sits

A submersible well pump is a sealed electric pump that sits underwater inside your well casing, usually 20 to 400 feet below ground. Unlike jet pumps that sit above ground and pull water up through a pipe, submersible pumps push water up from below. The motor and pump are housed together in a single waterproof unit that can operate fully submerged without damage.

The pump draws water from the aquifer around the well screen or intake, pressurizes it, and forces it up through a single discharge pipe to your house or pressure tank. Because the pump sits at the water source rather than trying to pull water from a distance, it can reach deeper wells and move larger volumes of water with less strain on the motor.

Key Takeaways

  • Submersible pumps sit underwater inside the well and push water upward, while jet pumps sit above ground and pull water down.
  • The pump has an intake at the bottom, a motor-driven impeller in the middle, and a discharge pipe running to the surface.
  • Water enters through a screen, gets pressurized by spinning impellers, and exits through a check valve that prevents backflow.
  • The pump is powered by a two-wire or three-wire electrical cable running down the well casing to the surface control box.
  • Submersible pumps work best in deep wells and can handle sandy or sediment-heavy water better than surface pumps.

The intake: where water enters the pump

At the bottom of the well, water surrounds the pump's intake section. The intake has a screen or strainer that filters out sand, gravel, and sediment before water enters the pump chamber. This screen is critical—if sand clogs it, the pump loses suction and can overheat.

The screen size depends on the well's geology. A well in sandy soil needs a finer screen than one in clay or bedrock. If the well was drilled poorly or the screen was never installed, sand will enter the pump and damage the impellers within weeks or months. This is why well maintenance includes periodic flushing to clear sediment buildup around the intake.

The impeller: how the pump pressurizes water

Inside the pump housing, a motor-driven shaft spins one or more impellers—curved metal or plastic wheels with blades. As the impeller spins (typically 3,450 revolutions per minute for a 60-hertz motor), it flings water outward and upward through a spiral chamber called a volute. This spinning motion converts the motor's rotational energy into pressure and velocity.

Most submersible pumps have multiple impeller stages stacked on top of each other. A single-stage pump can lift water about 25 feet and is used for shallow wells. A four-stage pump can lift water 100 feet or more. Each stage adds another impeller, so a pump for a 300-foot well might have 12 or more stages. The deeper the well, the more stages the pump needs to overcome the weight of the water column above it.

The impellers are sealed inside the pump housing and never contact the well water directly. Instead, the motor's cooling system circulates a small amount of water around the motor windings to keep it from overheating. If that seal fails and well water mixes with the motor oil, the motor will fail.

The discharge pipe and check valve: moving water to the surface

Water exits the top of the pump through a discharge pipe that runs the full length of the well to the surface. This pipe is usually 1 to 2 inches in diameter and is attached to the pump with a threaded connection. The pipe must be rigid enough to support its own weight plus the weight of water inside it—a 200-foot column of water weighs several tons.

At the pump outlet, a check valve allows water to flow upward but prevents it from flowing back down when the pump stops. Without this valve, water would drain back into the well every time the pump shuts off, wasting energy and putting stress on the motor at startup. The check valve is usually built into the pump head or installed just above it.

At the surface, the discharge pipe connects to a pressure tank or directly to your home's plumbing. A pressure switch on the tank tells the pump when to turn on and off based on water pressure, not on time or demand. When pressure drops below the switch setting (usually 30 to 40 pounds per square inch), the pump starts. When pressure reaches the upper limit (usually 50 to 60 psi), the pump stops.

The electrical system: power from the surface

Submersible pumps are powered by a cable that runs down the well casing alongside the discharge pipe. The cable is either two-wire (for 240-volt single-phase power) or three-wire (for 240-volt three-phase power). Three-phase pumps are more efficient and run cooler but require three-phase power, which is less common in residential wells.

At the surface, the cable connects to a control box that houses a pressure switch, a capacitor (for single-phase motors), and sometimes a soft-start device. The pressure switch monitors the pressure tank and signals the control box to energize the pump motor when water pressure drops. The capacitor provides the initial electrical boost needed to start a single-phase motor spinning.

The cable itself is specially designed for submersion and is rated for the depth and voltage of your system. A standard household extension cord will fail underwater. The cable insulation must resist moisture, UV damage (if exposed above ground), and the pressure of water at depth. Damage to the cable—from a well cap that doesn't seal properly, from rodents chewing it, or from age—is one of the most common reasons submersible pumps fail.

How depth affects pump performance

The deeper the well, the harder the pump must work to lift water to the surface. A pump rated for 300 feet can technically lift water from a 300-foot well, but it will do so slowly and use more electricity. The same pump in a 100-foot well will deliver water faster and use less power.

Pump manufacturers rate their products by gallons per minute (GPM) at a specific depth. A pump might deliver 15 GPM at 200 feet but only 10 GPM at 300 feet. If your well is deeper than the pump's rated depth, the pump will overheat and fail prematurely. This is why well testing before pump selection is essential—you need to know the static water level (where the water surface sits when the pump is off) and the pumping water level (where it drops to when the pump is running).

Common problems and why they happen

The most frequent failure in submersible pumps is sand infiltration. If the well screen is damaged, clogged, or was never installed, sand enters the pump and scores the impellers. The pump loses efficiency, draws more current, and eventually seizes. This is why wells should be developed (flushed) after drilling and periodically thereafter.

A second common problem is cable failure. The cable can be damaged by rodents, UV exposure, or straightforward age. Water seeping into the cable insulation causes a short circuit that trips the breaker or burns out the motor. Replacing a cable in a deep well is expensive and often means pulling the entire pump.

A third issue is loss of prime in the discharge pipe. If air enters the pipe (from a leak, a loose fitting, or a failed check valve), the pump cannot push water upward and will run dry. Running dry causes the motor to overheat because there is no water to cool it. A pressure gauge on the discharge line helps you spot this problem early.

Frequently Asked Questions

Can a submersible pump work in a shallow well?

Yes, but it is not ideal. Submersible pumps are designed for wells deeper than 25 feet. In shallow wells, a jet pump or centrifugal pump is usually cheaper and easier to service because you do not have to pull the pump from the ground. However, if your shallow well is in sandy soil or you need high flow, a submersible pump can work.

How long does a submersible pump last?

A well-maintained submersible pump typically lasts 8 to 15 years. Lifespan depends on water quality, how often the pump runs, and whether the well screen stays clean. Pumps in wells with high sediment or iron content fail faster. Pumps that run continuously (because the pressure tank is too small) also wear out sooner than those that cycle on and off.

What happens if the pump loses power?

When power is cut, the pump stops spinning and the check valve closes. Water in the discharge pipe stays in place rather than draining back into the well. The next time the pump starts, it must overcome the weight of that water column, which is why the motor draws extra current at startup. A soft-start device reduces this strain.

Why does my pump run but deliver no water?

The most likely cause is a clogged intake screen or a failed check valve. If the screen is blocked by sand or sediment, water cannot enter the pump. If the check valve is stuck open, water drains back into the well as fast as the pump pushes it up. A pressure gauge will show whether the pump is building pressure (check valve problem) or not (intake problem).

Can I install a submersible pump myself?

Installing a submersible pump requires lowering a heavy, expensive piece of equipment 50 to 400 feet into a narrow hole and making electrical connections that must be waterproof and safe. Most homeowners should hire a licensed well contractor. The cost of a professional installation (usually $500 to $2,000) is far less than the cost of a pump damaged during DIY installation or a fire from faulty wiring.