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Submersible pumps can work very well in rainwater tanks, cisterns, wells, and some IBC tote setups. But they have a few important downsides.
The biggest drawbacks are harder maintenance, electrical equipment sitting in the water, possible damage from running dry, and the need to pull the pump out when something goes wrong. They can also be a poor fit when the tank has a lot of sediment or the water level changes often.
The Main Downsides of a Submersible Pump
1. Maintenance Is Harder
A submersible pump sits underwater.
That keeps it out of sight and often makes it quieter. But it also makes inspection and repair less convenient.
If the pump clogs, loses pressure, or stops working, you may need to:
- Disconnect the power.
- Open the tank or cistern.
- Remove the discharge pipe or hose.
- Lift the pump out.
- Clean or repair it.
- Lower it back into place.
This is much more work than checking an external pump mounted beside a tank.
Large cisterns can make pump removal especially awkward. Never enter a tank or confined space to retrieve a pump unless the space has been evaluated and handled using proper confined-space safety procedures.
2. Running Dry Can Damage the Pump
Many submersible pumps depend on the surrounding water for cooling.
If the water level falls too low, the pump may continue running without enough water around it. This is called dry running.
Dry running can cause overheating and premature pump failure.
Rainwater systems are especially vulnerable because storage levels can change quickly during dry weather.
A suitable system may use:
- A low-water shutoff.
- A float switch.
- A level sensor.
- A pump controller with dry-run protection.
The pump and control system need to be compatible.
3. Sediment Can Cause Problems
Rainwater tanks often collect some fine sediment over time, even when gutters and prefilters are maintained.
A submersible pump near the bottom of a tank may draw this material into the intake.
Sediment can:
- Block the intake.
- Wear pump parts.
- Clog irrigation emitters.
- Load downstream filters more quickly.
- Reduce flow.
Keeping the intake above settled sediment can help.
Some systems use a floating intake so water is drawn from below the surface rather than directly from the tank floor.
Regular tank cleaning and good roof-runoff prefiltration are still important.
4. Electrical Safety Needs More Attention
A submersible pump is an electrical device operating in water.
That makes correct installation especially important.
The pump must be designed for submersible use. Power connections, controls, grounding, circuit protection, and wiring must also be suitable for the installation.
Do not use improvised electrical connections near a rainwater tank.
Outdoor electrical work may require weather-resistant equipment, ground-fault protection, and installation that meets local electrical requirements. A qualified electrician should handle work that goes beyond a simple manufacturer-approved plug-in setup.
5. Pump Failure Can Be Harder to Diagnose
With an external pump, you can often see and hear what the pump is doing.
A submerged pump is harder to inspect.
Low flow could come from:
- A blocked intake.
- Low tank level.
- A clogged filter.
- A pinched discharge line.
- An air or pressure-control problem.
- A damaged pump.
- A failing electrical connection.
- Excessive lift or pipe resistance.
You may have to remove the pump before you can confirm the cause.
6. The Pump Must Match the Required Head Height
A pump's advertised flow does not tell you how much water it will deliver in your actual system.
The pump also has to overcome head height.
Head height is the resistance the pump works against. It includes the vertical lift from the water level to the outlet plus losses through pipe, fittings, filters, valves, and other equipment.
A pump may deliver strong flow at low head but much less flow when pushing water uphill or through a restrictive system.
This matters when supplying:
- Garden irrigation.
- Elevated buildings.
- Pressure tanks.
- Filters.
- Long pipe runs.
- Several outlets.
Check the pump's performance curve rather than choosing it only by its maximum flow rating.
7. Pressure May Not Match the Application
Some submersible pumps are made mainly to move water. Others are designed to provide useful household or irrigation pressure.
Those are not the same job.
A pump that fills a nearby barrel quickly may still struggle with:
- Sprinklers.
- Long hoses.
- Drip systems with pressure regulators.
- Household fixtures.
- Treatment equipment that needs minimum pressure.
Flow rate is how much water the pump can move over a period of time.
Pressure is the force pushing that water through the system.
Both need to match the intended use.
8. Removing a Heavy Pump Can Be Difficult
Some submersible pumps are fairly heavy, especially when connected to pipe or hose.
The pump should not normally be lifted by its electrical cord.
A suitable lifting rope, cable, or retrieval system may be needed depending on the pump design.
Deep cisterns can make servicing more complicated.
Plan how the pump will be removed before installing it.
9. Tank Access Can Become a Problem
A submersible pump needs to fit through the tank opening.
This sounds simple, but it can become an issue with:
- Narrow inspection ports.
- IBC tote openings.
- Internal tank supports.
- Fixed plumbing.
- Large pump bodies.
- Float switches that need room to move.
Understanding drawbacks of rainwater harvesting helps verify installation details that support reliable daily use.
Check the pump dimensions before installation.
Also make sure the pump can be removed later without cutting pipes or dismantling half the system.
10. Float Switches Need Space
Many submersible pumps use a float switch to turn the pump on or off.
A float needs enough room to move freely.
It can sometimes catch on:
- Tank walls.
- Pipes.
- Cables.
- Pumps.
- Internal braces.
This can prevent the pump from turning on or shutting off correctly.
A stuck float can be particularly troublesome if it allows the pump to continue running after the water level drops.
11. Leaks Can Be Less Obvious
A leak in the discharge plumbing inside a tank may be difficult to notice.
Water can simply circulate back into the tank instead of reaching the outlet.
You might see:
- Lower pressure.
- Longer pump run times.
- Weak irrigation flow.
- Unexpected cycling.
Because the leak is underwater, there may be no visible puddle.
Connections inside the tank should be secure and suitable for submerged use.
12. Repairs Often Mean Replacing the Pump
Some small submersible pumps are not designed for easy field repair.
If the motor, seals, or internal electronics fail, replacing the entire pump may be more practical than repairing it.
This can make a submersible pump less convenient for systems where easy serviceability is a priority.
13. Water Quality Still Matters
A submersible pump moves water. It does not make the water clean or safe.
Roof runoff can contain sediment, organic matter, bird droppings, insects, microorganisms, roof material residues, and other contaminants.
For garden watering, treatment needs may be fairly simple depending on the irrigation equipment and crops involved.
Household reuse may require additional filtration and controls.
Drinking-water use requires a much more careful whole-system approach that can include suitable collection surfaces, debris removal, first-flush management, treatment, current laboratory testing, maintenance, and compliance with applicable local requirements.
Do not treat the pump itself as a water-treatment step.
14. Freeze Protection Can Still Be Necessary
Putting the pump underwater does not automatically make the entire installation freeze-safe.
Exposed components may still freeze, including:
- Discharge pipes.
- Hoses.
- Valves.
- Filters.
- Check valves.
- Pressure controls.
Frozen plumbing can block water flow or damage fittings and equipment.
Systems in freezing climates need a planned winter setup based on the tank location, pipe depth, drainage arrangement, and intended winter use.
When a Submersible Pump Makes Sense
Despite the drawbacks, submersible pumps are often a good choice when you want the pump inside the storage tank.
They can work well for:
- Underground cisterns.
- Large rainwater tanks.
- Quiet installations.
- Systems where an external pump would have suction problems.
- Applications requiring the pump to push water upward from storage.
Because the pump pushes water instead of pulling it through a suction line, it can avoid some of the priming problems associated with surface pumps.
When an External Pump May Be Easier
An external pump may make more sense when easy access is important.
Consider one when:
- The tank is above ground.
- The pump can be mounted close to the tank outlet.
- Regular servicing is expected.
- The system needs easy winterization.
- You want to inspect the pump without opening the tank.
- The storage level stays high enough for reliable suction.
External pumps have their own limitations, including priming, suction lift, noise, and possible air leaks.
The better choice depends on the entire system rather than the pump type alone.
What to Check Before Using a Submersible Pump
Before choosing one, check how the pump fits the rest of the system.
Important questions include:
- How low can the tank level get?
- Does the pump have dry-run protection?
- How much vertical lift is required?
- What flow and pressure do you need?
- How long is the discharge pipe?
- Are filters or pressure regulators installed?
- Is there sediment near the tank bottom?
- Can the pump fit through the access opening?
- Can it be removed easily for service?
- Is the electrical setup suitable for a wet outdoor location?
- Will exposed plumbing need freeze protection?
A pump that fits these conditions is much more likely to work reliably than one chosen only by horsepower or maximum flow.
Frequently Asked Questions
Are submersible pumps better than external pumps for rainwater tanks?
Not always. Submersible pumps are quiet and avoid many suction and priming problems. External pumps are usually easier to inspect and service. The better option depends on tank location, water level, required pressure, maintenance access, and climate.
Can a submersible pump sit directly on the bottom of a rainwater tank?
It may be physically possible, but the bottom is often where sediment collects. Drawing from slightly above the bottom or using an appropriate intake arrangement may reduce sediment entering the system.
What happens if a submersible pump runs without water?
Some pumps can overheat or suffer internal damage. Dry-run protection, a low-level switch, or another suitable control can help prevent this.
Can I use a submersible pump with an IBC tote?
Sometimes. Check the pump dimensions, access opening, electrical requirements, discharge connection, float-switch clearance, and required flow and pressure. IBC totes can also accumulate sediment, so intake position matters.
Are submersible pumps good for garden irrigation?
They can be. The pump must provide enough flow and pressure for the irrigation system. Long hoses, sprinklers, drip regulators, filters, and elevation changes all affect performance.
Do submersible pumps need filters?
The pump itself may have an intake screen, but that does not replace proper rainwater-system filtration. The amount and type of filtration depend on the stored water quality and how the water will be used.
The drawbacks of submersible equipment should be weighed against whether rainwater tanks need pumps for the required pressure.
Are submersible pumps safe in drinking-water systems?
Only pumps specifically suitable for the intended water application should be considered. More importantly, a pump does not make collected rainwater potable. Drinking-water systems require appropriate collection, treatment, testing, maintenance, and compliance with local requirements.
