What a Submersible Well Pump Does and Where It Sits

A submersible well pump is a sealed electric motor and pump combined into one unit that sits underwater at the bottom of your well. Unlike jet pumps that sit above ground and pull water up through a pipe, a submersible pump pushes water up from below. The motor and pump are sealed together so water cannot enter the electrical parts, and the whole assembly hangs from a pipe or cable that runs up to your house.

The pump sits deep in the well — often 50 to 400 feet down, depending on how far down your water table is. Because it works by pushing rather than pulling, it can reach much deeper water than surface pumps can. The deeper your well, the more likely you have a submersible pump instead of a jet pump or hand pump.

Key Takeaways

  • A submersible pump combines a sealed electric motor and pump into one waterproof unit that hangs at the bottom of your well.
  • The motor spins an impeller (a fan-like wheel) that forces water upward through a pipe to your house, rather than pulling water from above ground.
  • Power reaches the pump through an electrical cable that runs down the well alongside the discharge pipe.
  • The pump works continuously as long as power flows and water is present, and a pressure tank at the surface stops it when your house has enough water pressure.
  • Submersible pumps can reach much deeper water than surface pumps because they push water instead of trying to pull it.

The Motor and Impeller: How Water Gets Pushed Upward

Inside the sealed housing, an electric motor spins a shaft connected to an impeller — a wheel with curved blades or fins. As the impeller spins, it forces water outward and upward, much the way a fan blade pushes air. The impeller is not a screw or auger; it is a centrifugal design that relies on spinning motion to move water.

The water enters the pump from the bottom or side, gets caught by the spinning impeller, and is forced into a discharge pipe that runs straight up the well. The faster the motor spins, the more water it moves and the higher the pressure it creates. Most household submersible pumps spin at 3,450 revolutions per minute (rpm) on standard 60-hertz household current, though some run at 1,750 rpm for lower flow rates.

The pump does not work like a syringe that fills and empties. It works continuously — as long as the motor is running and water surrounds the impeller, water keeps moving upward. If the water level drops below the pump intake, the pump will run dry and can overheat, which is why many wells have a low-water cutoff switch that stops the motor if the water level falls too far.

The Discharge Pipe and Pressure Tank: Getting Water to Your House

Water pushed up by the impeller travels through a discharge pipe that runs from the pump all the way to the surface. This pipe is typically 1 to 1.5 inches in diameter and may be plastic, steel, or copper. At the top of the well, the pipe connects to a pressure tank — a metal or plastic tank that holds pressurized water and air.

The pressure tank serves two jobs. First, it stores water so the pump does not have to run every time you turn on a faucet. Second, it maintains water pressure throughout your house. As water fills the tank, air inside gets compressed. When you open a faucet, the compressed air pushes water out. Once the pressure drops to a set point (usually around 40 pounds per square inch), a pressure switch turns the pump back on to refill the tank.

Without a pressure tank, the pump would start and stop dozens of times a day, wearing out the motor and switch much faster. The tank also protects against water hammer — the loud bang you hear in pipes when water flow suddenly stops — by absorbing the shock of pressure changes.

The Electrical Cable: Power Down the Well

Power reaches the submersible pump through a heavy-duty electrical cable that runs down the well alongside the discharge pipe. This cable is not the same as household extension cord wire. It is submersible pump cable, rated for continuous immersion in water and designed to carry the amperage the pump motor needs — typically 15 to 30 amps for a household pump.

The cable connects at the surface to a pressure switch and a check valve, then to your home's electrical panel or a dedicated circuit breaker. The pressure switch is the brain of the system: it senses water pressure in the tank and tells the pump when to turn on and off. A check valve — a one-way valve in the discharge line — prevents water from flowing backward down the pipe when the pump stops, which would drain the tank and waste energy on the next startup.

If the cable gets damaged or water enters the connection, the pump will not run and the motor can be ruined. This is why the cable must be properly sealed where it enters the well and protected from sharp edges or rocks that could cut the insulation.

How the Pump Knows When to Turn On and Off

A pressure switch mounted near the pressure tank controls when the pump runs. It contains a spring and a metal diaphragm that responds to water pressure. You set two pressure points: the cut-in pressure (when the pump turns on, usually 40 psi) and the cut-out pressure (when the pump turns off, usually 60 psi).

Here is the cycle: You turn on a faucet and water flows from the pressure tank. As the tank empties, pressure inside drops. When pressure falls to 40 psi, the switch closes an electrical contact, sending power to the pump motor. The pump runs and pushes water back into the tank. As pressure rises, the switch senses it. When pressure reaches 60 psi, the switch opens the contact and cuts power to the pump. The pump stops, and the compressed air in the tank keeps water flowing to your faucets until pressure drops again.

This on-off cycle repeats throughout the day. If you use a lot of water quickly, the pump may run for several minutes without stopping. If you use very little water, the pump might run for only a few seconds before the tank fills and pressure rises enough to shut it off.

Common Problems and Why They Happen

The most common failure in a submersible pump system is a loss of prime — the pump loses contact with water and starts pulling air instead. This usually happens when the water level drops below the pump intake, or when a leak in the discharge pipe lets air in. A pump running dry will overheat and burn out the motor in minutes.

Another frequent issue is a failed check valve. If the check valve leaks, water drains out of the discharge pipe and tank when the pump stops. The next time the pump starts, it has to refill the entire pipe before water reaches your house, which wastes energy and can cause air to enter the system.

Pressure switch failure is also common. If the switch does not open when pressure is high enough, the pump keeps running and can overpressurize the tank. If the switch does not close when pressure drops, the pump never runs and you have no water. A faulty switch is usually cheaper to replace than a pump motor.

Sediment and sand in the well water can wear down the impeller over time, reducing flow and pressure. This is why many wells have a sediment filter or screen at the pump intake. If the screen clogs, the pump cannot draw water and will run dry.

Depth and Pressure: Why Submersible Pumps Work So Deep

A surface pump (like a jet pump) works by creating a vacuum that pulls water up. Atmospheric pressure limits how high a vacuum can pull water — roughly 25 feet in ideal conditions. A submersible pump does not rely on a vacuum. It pushes water up from below, so depth is limited only by the pump's power and the strength of the discharge pipe.

A typical household submersible pump can push water up 200 to 400 feet, depending on the model and how much water you need per minute. Deeper wells need more powerful pumps, which cost more and use more electricity. The deeper the well, the longer the discharge pipe, and the more pressure the pump must create to overcome the weight of water in that pipe.

This is why submersible pumps are standard for deep wells. If your well is more than 30 feet deep, a submersible pump is almost always the right choice. Shallower wells may use a jet pump or hand pump, but submersible pumps work at any depth and are reliable for decades if maintained properly.

Frequently Asked Questions

Can a submersible pump run dry, and what happens if it does?

Yes, and it will overheat and fail quickly. A pump running dry has no water to cool the motor. Most pumps will burn out the motor windings in 5 to 15 minutes. This is why a low-water cutoff switch is important — it stops the pump if the water level drops too far, protecting the motor from damage.

How long does a submersible pump usually last?

A well-maintained submersible pump typically lasts 8 to 15 years. Lifespan depends on water quality, how often the pump runs, and whether sediment or sand damages the impeller. Pumps in sandy wells wear out faster than those in clean wells. Regular filter maintenance and keeping the pressure tank in good condition extend pump life.

What is the difference between a 1-wire and 3-wire submersible pump?

A 1-wire pump has the pressure switch built into the pump itself, so only one electrical wire runs down the well. A 3-wire pump has the pressure switch at the surface, so three wires run down the well to control the motor. 3-wire pumps are more common in modern installations because the surface switch is easier to replace if it fails.

Why does my pump keep running even when I am not using water?

A leaking check valve is the most common cause. If the check valve does not seal properly, water drains out of the tank when the pump stops. Pressure drops, the switch turns the pump back on, and the cycle repeats. A failed pressure switch that does not open at the right pressure can also cause this. Both parts are replaceable without replacing the pump.

Can I install a submersible pump myself?

Installation requires lowering a heavy pump down a narrow well, connecting electrical cable safely, and setting up the pressure switch and check valve correctly. Most homeowners hire a licensed well contractor for this work. Improper installation can damage the pump, create electrical hazards, or leave the system unable to deliver water. If you are experienced with well systems, you can do some maintenance like filter changes, but the initial setup is best left to a professional.