What Is a Submersible Pump? | Sealed Below The Waterline

A submersible pump is a sealed pump-and-motor unit designed to run fully underwater, pushing liquid to the surface instead of pulling it.

For the full breakdown, see our best 2-Inch Submersible Pump guide.

Ask what a submersible pump is and the short answer is in the name: the whole assembly, motor included, sits below the fluid level inside the water it moves. Because it operates submerged, it pushes liquid up to the surface rather than relying on suction to draw it upward. That single design choice makes it the workhorse of drainage, sewage, and clean-water service, and it is why you rarely need to prime one before it runs.

How A Submersible Pump Works

The pump uses an impeller driven by a sealed electric motor. As the impeller spins, centrifugal force flings liquid outward from the inlet to the discharge pipe, creating enough pressure to push the fluid up and out. Grundfos describes the unit as suitable for submerged installation in clean-water service, which covers everything from basement sumps to irrigation systems.

The motor housing is watertight, often hermetically sealed, so the electrical parts can sit safely underwater during normal operation. Since the pump is already positioned below the waterline, gravity does the priming work for you — there is no suction lift to establish before flow starts.

Common Types And What Each One Moves

Not every submersible pump handles the same liquid, and using the wrong one is a fast way to burn out the unit. The two broad categories are clean-water pumps and wastewater pumps, and the distinction matters more than most buyers expect.

• Clean-water submersible pumps handle clear water with little to no solids — think rainwater tanks, flooded basements, or irrigation supply.
• Submersible wastewater pumps are a specialized subtype built for sewage and wastewater duty. KSB notes these are single-stage, overhung centrifugal pumps closed-coupled to a submersible motor, available in diffuser or volute designs.
• Domestic sewage units often add a float switch that starts the pump when water rises to a set level and shuts it off again once the water drops back down.

If your job involves solids or sewage, a clean-water pump will clog or fail. Wastewater pumps move that material reliably but are overkill for pumping clear water.

Installing And Running One Safely

Install the pump fully submerged in the liquid it is meant to move, and connect the discharge piping or hose to the outlet before powering it up. If the model uses a float switch, set it so the pump cycles on and off at the water levels your application needs.

Electrical safety is the part you cannot skip. The motor and wiring operate while immersed, so a damaged cable, gland, or seal creates shock and failure risks. Australian regulator guidance for submersible pumps covers appliances handling liquids up to 90°C and includes portable and fixed units with electrical parts partly or fully immersed during normal use — check that your cable entry and seals are rated for submerged service and stay undamaged. If you are sizing a unit for a specific job, KSB’s technical library covers the engineering details, and a practical 2-inch submersible pump roundup can help match one to your project.

One more compatibility note: a wastewater-rated pump is for wastewater duty, not every water-moving job. Match the pump to the liquid, keep the electrical parts sound, and the unit will run for years without complaint.