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What Pump Is Commonly Used for Transferring Water?
A centrifugal pump is one of the most commonly used pumps for transferring water from one place to another.
It works well for moving relatively clean water between tanks, cisterns, rain barrels, ponds, and other storage containers. Centrifugal pumps are popular because they can move a useful amount of water without being overly complicated.
However, the best pump depends on where the water is stored, how far it must travel, and how high it must be lifted.
Common Pumps Used for Water Transfer
Several pump types can transfer water, but they are suited to different setups.
| Pump type | Common use | Main advantage |
|---|---|---|
| Centrifugal pump | Tank-to-tank transfer, irrigation, general water movement | Good flow for general use |
| Submersible pump | Cisterns, tanks, wells, sumps | Operates underwater |
| Utility pump | Temporary draining and transfer jobs | Simple and portable |
| Self-priming transfer pump | Rainwater tanks and portable transfer systems | Easier startup when the pump is above the water |
| Diaphragm pump | Small systems, cabins, RV-style plumbing | Can provide pressure at relatively low flow |
For many rainwater systems, the choice comes down to a surface-mounted centrifugal pump or a submersible pump.
Why Centrifugal Pumps Are So Common
A centrifugal pump contains a spinning part called an impeller. The impeller moves water through the pump and pushes it into the discharge pipe.
These pumps are often used because they can provide:
- Steady water flow
- Moderate to high transfer rates
- Simple installation
- Compatibility with common hoses and pipes
- Enough pressure for many garden and transfer jobs
A centrifugal pump may be used to move rainwater from a storage tank to another tank, supply an irrigation line, or transfer stored water to a point of use.
Not every centrifugal pump works the same way, though. Some must be filled with water before starting, while others are designed to be self-priming.
When a Submersible Pump Makes More Sense
A submersible pump sits directly in the water.
It is often a good choice for a large rainwater tank or underground cistern because the pump does not have to pull water up through a suction pipe. It pushes water from the tank instead.
This can simplify some installations and reduce problems associated with suction lift.
Submersible pumps are commonly used when:
- The storage tank is deep
- The pump can remain inside the tank
- A quiet installation is important
- The water needs to be pushed uphill or through a longer pipe
- There is no convenient location for a surface pump near the tank
The pump still needs to be suitable for the water quality and intended use. Sediment can shorten pump life if the pump repeatedly draws debris from the bottom of a rainwater tank.
What Is a Water Transfer Pump?
The term transfer pump describes what the pump does rather than one specific pump design.
A water transfer pump simply moves water from one location to another.
For example, you might use one to move water:
- From an IBC tote to a garden tank
- From a rainwater tank to an irrigation system
- Between two storage tanks
- From a temporary container into a cistern
- From a pond or reservoir to another location
A transfer pump may be centrifugal, submersible, diaphragm, or another design.
That is why choosing a pump based only on the words "water transfer pump" is not enough. Its flow, pressure, lift, connections, and operating limits still need to match the system.
Flow Rate Matters
Flow rate is the amount of water a pump can move during a certain amount of time. It is often stated in gallons per minute, or GPM.
A pump used only to transfer water between tanks may benefit from a higher flow rate because faster transfer saves time.
But more flow is not always better.
The piping must be large enough to carry that flow without creating excessive resistance. Small hoses, long pipe runs, filters, valves, and fittings can all reduce the actual flow reaching the other end.
The flow shown for a pump also usually drops as the pump has to push water higher.
Head Height Matters Too
Head height describes how much resistance the pump must overcome, especially from lifting water vertically.
If water must travel from a tank at ground level to another tank uphill, the pump needs enough head capacity to make that lift.
The system also has resistance from:
- Pipe length
- Small pipe diameter
- Elbows
- Valves
- Filters
- Check valves
- Hose fittings
A pump that moves plenty of water through a short, level hose may move much less water through a long uphill pipe.
When comparing pumps, look at the manufacturer's pump curve rather than relying only on the maximum flow number.
A pump curve shows how much flow the pump can provide at different head levels.
Surface Pump or Submersible Pump?
A simple way to choose between them is to consider where the pump will sit.
Choose a surface pump when:
- The pump can be installed close to the tank
- You want easy access for maintenance
- The suction lift is within the pump's operating limits
- The pump is protected from rain and flooding if required
- The pump can be properly primed
Choose a submersible pump when:
- The pump can safely remain inside the tank
- The storage tank is deep
- Suction lift would be difficult
- You want the pump hidden from view
- The pump is designed for continuous or repeated submerged use
Both can work well. System layout usually determines which arrangement is easier.
Self-Priming Pumps Can Simplify Tank Transfer
A pump installed outside a tank may need to pull water through a suction hose before it can begin pumping.
Many standard centrifugal pumps cannot pump air effectively. The pump housing and suction line may need to contain water before startup. This is called priming.
A self-priming pump is designed to handle this startup process more easily after it has been initially filled according to the manufacturer's instructions.
Self-priming pumps are common in above-ground rainwater systems because the pump may sit beside the tank rather than below the tank's water level.
Even a self-priming pump has limits. A leaking suction connection, excessive lift, blocked intake, or empty tank can prevent proper operation.
Pay Attention to the Suction Side
The suction side of a surface pump is especially important.
Air leaking into the suction pipe can cause poor performance even when no water leaks out.
Keep the suction line:
- Properly sealed
- As short as practical
- Within the pump's allowed diameter
- Free of unnecessary restrictions
- Within the pump's permitted suction-lift range
Do not assume a smaller hose is acceptable just because an adapter makes it physically fit.
Restricting the inlet can reduce performance and may contribute to pump problems.
Match the Connections Before Buying a Pump
Check whether rainwater tanks need pumps to understand symptoms of trapped air during pump operation.
A pump must physically connect to the rest of the water system.
Check the:
- Pump inlet size
- Pump outlet size
- Tank outlet size
- Hose or pipe diameter
- Thread type
- Fittings and adapters
- Valves
- Filters or strainers
For rainwater tanks, the outlet may pass through the tank wall using a bulkhead fitting.
A bulkhead fitting creates a sealed connection through the wall of a tank. Its size does not automatically determine the ideal pump size, but it can limit how easily water reaches the pump.
Avoid reducing a large pump inlet to a very small tank outlet unless the pump manufacturer confirms that arrangement is acceptable.
Protect the Pump From Sediment
Rainwater storage tanks can collect dirt, roof debris, and fine sediment.
A pump should not continuously draw from the dirtiest part of the tank if that can be avoided.
Depending on the system, protection may include:
- Gutters and screens that keep larger debris out
- A suitable prefilter before water enters storage
- A floating intake
- An intake positioned above settled sediment
- A pump-compatible inlet strainer
A first-flush diverter can also be part of a rainwater collection system. It diverts some of the initial roof runoff, which may carry a higher load of roof debris and contamination.
Pump protection and water treatment are separate issues. A strainer that protects a pump does not by itself make rainwater safe to drink.
Do Not Let the Pump Run Dry
Many water pumps depend on the water passing through them for cooling or lubrication.
Running a pump without water can damage it.
This can happen when:
- A rainwater tank becomes empty
- A suction pipe loses its prime
- An intake becomes blocked
- A valve is accidentally closed
- An automatic system continues calling for water after storage is depleted
For frequently used systems, dry-run protection can be valuable.
Some systems use float switches, level controls, pressure controls, or pump controllers to stop the pump when water is unavailable.
The control must be compatible with the pump and its electrical requirements.
Consider Pressure if the Pump Feeds Irrigation
Moving water into another open tank mainly requires flow and enough head to reach the destination.
Supplying sprinklers or other pressure-dependent equipment is different.
The pump must provide both:
- Enough flow for the irrigation zone.
- Enough pressure after pipe and elevation losses.
A high-flow transfer pump may not provide the pressure required by a sprinkler system.
Likewise, a high-pressure pump may be unnecessary if the only job is transferring water through a short hose into another tank.
Choose the pump for the actual job rather than the largest advertised number.
Power Supply Can Affect the Choice
Water transfer pumps may use:
- Household AC electricity
- Low-voltage DC power
- Solar-powered electrical systems
- Engine-driven power
For a fixed home rainwater system, an electric centrifugal or submersible pump is common.
Remote tanks and small off-grid systems may require a different approach.
Check the pump's electrical requirements before installation. Outdoor electrical equipment needs suitable protection for its location. Permanent wiring, wet-location electrical work, and higher-power pump installations may require a qualified electrician.
Think About Freezing Weather
Water trapped inside a surface pump, filter housing, hose, or exposed pipe can freeze.
Freezing water expands and can crack equipment.
In climates that freeze, the system needs a winter plan. This may involve draining exposed components, locating equipment in a protected space, or using a system specifically designed for the local conditions.
Do not assume that insulation alone will prevent freezing during extended cold weather.
Submersible pumps may be less exposed to outdoor air temperatures, but pipes and fittings leaving the tank can still freeze.
Which Pump Should You Use for Rainwater Transfer?
For simple tank-to-tank rainwater transfer, a centrifugal water transfer pump is often a practical choice when it can be installed near the tank and within its suction limits.
A submersible pump can be a better choice when the pump will sit inside a cistern or large storage tank.
Before choosing either one, determine:
- Where the pump will be located.
- How high the water must be lifted.
- How far it must travel.
- How much flow you need.
- What pipe or hose size will be used.
- Whether pressure is needed at the destination.
- What electrical supply is available.
- How the pump will be protected from sediment and dry running.
Once those details are known, the manufacturer's pump curve can show whether a particular pump can deliver the needed flow under your actual conditions.
Frequently Asked Questions
What type of pump is most commonly used to transfer water?
A centrifugal pump is one of the most common choices for general water transfer. It is widely used for moving water between tanks and supplying irrigation systems.
Can I use a submersible pump to transfer rainwater?
Yes. A submersible pump can move water directly from a rainwater tank or cistern. It can be especially useful for deep tanks or installations where a surface pump would have difficulty pulling water through a suction pipe.
What is the difference between a transfer pump and a pressure pump?
A transfer pump is mainly selected to move water from one place to another. A pressure pump is selected to maintain enough pressure for equipment such as faucets, irrigation devices, or other fixtures. Some pumps can perform both jobs when properly sized.
How big should a water transfer pump be?
Size it according to the required flow, vertical lift, pipe resistance, and desired pressure. Maximum advertised flow alone is not enough. Use the pump manufacturer's flow-versus-head curve to check expected performance.
Does a transfer pump need to be primed?
Some surface-mounted centrifugal pumps do. The pump and suction line may need to contain water before startup. Self-priming pumps are designed to simplify this process, although they still must be installed within their operating limits.
Can a water pump pull water from any depth?
No. Surface pumps have limits on how far they can lift water through the suction side. Actual performance also depends on the installation and operating conditions. Deep applications commonly use submersible pumps that push water upward instead.
Should I put a filter before my rainwater pump?
A suitable strainer or intake arrangement can help keep debris out of the pump, but the correct setup depends on the pump manufacturer and the water system. Avoid installing a restrictive filter on the suction side unless it is appropriate for the pump. Pump protection does not make collected rainwater potable.
