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Choosing the right pump starts with one simple question: What do you need the water to do?
A pump for filling a watering can has very different needs from a pump that must run sprinklers, move water uphill, or supply several fixtures in a cabin.
The right pump must provide enough flow and pressure for the job without being much larger than the system needs. It also has to match your tank, pipe size, power supply, water quality, and installation location.
Start With How You Will Use the Water
Before comparing pump types, list what the pump will supply.
Common rainwater uses include:
- Watering a garden with a hose
- Running drip irrigation
- Supplying sprinklers
- Moving water from one tank to another
- Filling a day tank
- Washing tools or outdoor areas
- Supplying toilets or other approved household uses
- Feeding a treatment system
The pump that works well for one task may perform poorly at another.
For example, drip irrigation may need modest flow but controlled pressure. A sprinkler system may need much more flow and pressure. Moving water between two large tanks may require high flow but little outlet pressure.
Start with the job, then size the pump around it.
Understand Flow Rate
Flow rate tells you how much water a pump can move over a certain amount of time. It is often shown in gallons per minute, or GPM.
Your pump needs to supply enough flow for everything that may run at the same time.
For example, imagine you want to operate two irrigation zones, but only one zone will run at a time. You size the pump for the larger zone, not both zones combined.
If several fixtures may run together, their required flow rates need to be considered together.
Do not assume that a pump's maximum advertised flow is what you will actually get. Pump flow normally drops as the pump has to work against more height, pressure, pipe resistance, fittings, and filters.
This is why the pump's performance curve matters more than its maximum flow number.
Understand Head Height
Head height is a way of describing how hard the pump must work to move water.
It includes more than just the vertical distance between the tank and the outlet.
The pump must overcome:
- Vertical lift
- Desired outlet pressure
- Resistance inside pipes
- Elbows and valves
- Filters
- Check valves
- Long pipe runs
- Other restrictions
A pump that can move plenty of water across a flat yard may provide much less flow when pumping uphill.
When manufacturers list pump performance, they often show flow at different amounts of head. Look for the point on the pump curve that matches your system rather than choosing a pump only by its maximum head or maximum flow.
Decide How Much Pressure You Need
Pressure matters when the water must come out of a hose, sprinkler, appliance, or fixture with enough force to work properly.
Gravity-fed rain barrels may provide enough pressure for some drip systems or slow watering jobs, especially when the outlet is well below the water level. They usually do not provide the same pressure as a powered pump.
A pump becomes more important when you want to:
- Use a normal garden hose over a longer distance
- Run sprinklers
- Push water uphill
- Supply pressure-dependent irrigation equipment
- Send water through restrictive filtration
- Supply fixtures that require steady pressure
Check the pressure requirements of anything connected after the pump. More pressure is not always better. Excessive pressure can damage tubing, irrigation parts, filters, and fittings.
A pressure regulator may be needed when the pump can produce more pressure than downstream equipment can safely handle.
Choose the Right Pump Type
Several pump styles can work in rainwater systems.
Submersible Pumps
A submersible pump sits inside the tank.
These pumps can be a good choice when you want:
- Quiet operation
- A clean installation
- Less trouble getting the pump primed
- Water pushed from inside a cistern or larger storage tank
Because the pump is underwater, it pushes water rather than pulling it through a suction pipe.
Installation and servicing can be less convenient because the pump must be removed from the tank when it needs attention.
Any electrical installation around water should follow the manufacturer's instructions and applicable electrical requirements. Use qualified help when the installation goes beyond simple plug-in equipment.
Surface Pumps
A surface pump sits outside the tank and draws water through a suction line.
This arrangement makes the pump easier to inspect and service.
A surface pump can work well for:
- Garden irrigation
- Tank-to-tank transfer
- Small rainwater systems
- Installations where easy pump access matters
The suction side must be designed carefully. Air leaks, excessive lift, clogged strainers, or poor pipe sizing can make it difficult for the pump to prime or maintain flow.
Some pumps are self-priming, but "self-priming" does not mean they can overcome every suction problem.
Transfer Pumps
Transfer pumps are mainly designed to move water from one place to another.
They can be useful for:
- Emptying a temporary tank
- Moving water between IBC totes
- Filling another storage tank
- Draining equipment
A transfer pump is not automatically a good pressure pump for sprinklers or household-style water service. Check how much flow it can provide at the pressure your actual application requires.
Booster and Pressure Pumps
A booster or pressure pump is designed to provide more consistent pressure to fixtures or irrigation equipment.
These systems often use a pressure switch, controller, or pressure tank to start and stop the pump as water is used.
They can make sense for larger rainwater systems where you want water service to behave more like a conventional pressurized supply.
The controls need to match the pump and intended use. Frequent starting and stopping can shorten pump life if the system is poorly sized.
Check the Vertical Lift
Measure the vertical difference between the water source and the highest point where the pump must send water.
For a surface pump, also pay close attention to how far the pump must lift water on the suction side.
Suction lift is harder on a pump than pushing water after it reaches the pump.
Whenever practical, a surface pump should be installed close to the tank and low enough to keep the suction lift short.
Also remember that the tank's water level changes. A pump may work well when a cistern is full but face a greater lift when the water level drops.
Size the system for realistic low-water conditions, not just a full tank.
Include Pipe Length and Pipe Size
Long or narrow pipes create resistance.
That resistance reduces the flow available at the far end of the system.
Small pipe is especially restrictive when flow is high.
When planning a pump system, consider:
- Total pipe length
- Inside diameter of the pipe
- Number of elbows
- Valves
- Filters
- Elevation changes
- Required flow
Using a larger pipe where appropriate can sometimes improve performance more effectively than installing a larger pump.
Avoid assuming that the pump's outlet size determines the best pipe size for the entire system. A long run may benefit from larger pipe even if the pump connection itself is smaller.
Look at the Pump Curve
A pump curve is one of the most useful tools for choosing a pump.
It shows approximately how much water the pump can deliver at different amounts of head.
Usually, as head increases, flow decreases.
For example, a pump may have a high maximum flow when almost no resistance is present. That same pump may deliver much less water when pushing uphill through a long pipe and several filters.
Find your estimated system head, then check the pump curve to see the expected flow at that point.
Do not size a pump based only on:
- Maximum flow
- Maximum pressure
- Maximum head
Those numbers usually represent different ends of the pump's operating range. You generally cannot get maximum flow and maximum pressure at the same time.
Make Sure the Pump Can Handle the Water
Rainwater can carry small amounts of dirt, organic matter, roof debris, and tank sediment.
Most pressure pumps work better with reasonably clean water.
Good system design normally keeps debris away from the pump through measures such as:
- Gutter screens
- Inlet screening
- First-flush diversion when appropriate
- Tank inlet controls
- Pump strainers
- Floating intakes
- Settling space
A first flush device diverts some of the earliest roof runoff from a rain event, when roof debris may be most concentrated.
Avoid placing a pump intake directly in heavy sediment at the bottom of a tank unless the pump is specifically intended for that condition.
Do not assume that pumping or filtering rainwater makes it safe to drink. Drinking-water use requires suitable collection, treatment, maintenance, current water testing, and compliance with applicable local requirements.
Check Connection Sizes
Before buying a pump, confirm how it will connect to the rest of the system.
Look at:
- Pump inlet size
- Pump outlet size
- Tank outlet size
- Hose or pipe diameter
- Thread type
- Fittings
- Valves
- Filter connections
An IBC tote, rain barrel, cistern, and pump may all use different connections.
A bulkhead fitting is a sealed fitting that passes through the wall of a tank. It is commonly used to create a secure inlet or outlet connection.
Reducing pipe size too aggressively can restrict flow. Adding many small adapters also creates more places for leaks and resistance.
Reviewing water-pump selection factors helps compare manufacturer ratings for frequent pump operation.
Plan the connection path before choosing the pump.
Match the Pump to Your Power Supply
Pumps may run from household electricity, batteries, generators, or solar-based power systems.
Check:
- Voltage
- Running power demand
- Starting power demand
- Cord and circuit requirements
- Controller requirements
- Availability of power near the tank
Pump motors may briefly need more power when starting than when running.
That matters when using an inverter, generator, battery system, or solar setup.
Do not assume a solar panel can be connected directly to any electric pump. Solar pumping systems may need suitable controllers, wiring, protection, batteries, or other equipment depending on their design.
Electrical equipment used around tanks and wet areas should be installed in a way that is suitable for the environment.
Protect the Pump From Running Dry
Many pumps can be damaged if they operate without enough water.
This is called dry running.
Rainwater tanks are especially likely to run low because the stored supply depends on rainfall and water use.
Useful protection may include:
- Float switches
- Low-water sensors
- Dry-run protection built into the pump or controller
- Properly placed intake lines
Do not rely only on remembering to switch the pump off.
Automatic protection becomes more important when irrigation systems or pressure controls can start the pump while nobody is watching.
Think About Pump Cycling
Pressure pumps often start when pressure drops and stop when the target pressure returns.
If the system causes the pump to start and stop every few seconds, it is called short cycling.
Frequent cycling can increase wear.
A pressure tank, correctly sized controller, variable-speed pump, or other system design may help reduce unnecessary cycling, depending on the setup.
This matters especially for applications with small or changing water demands.
For example, a large pump feeding one tiny drip line may cycle repeatedly unless the system includes suitable controls.
Consider Filters and Treatment Equipment
Filters add resistance to water flow.
That resistance may increase as the filter collects debris.
If your system includes filtration after the pump, include that pressure loss when evaluating the pump.
This may matter with:
- Sediment filters
- Fine cartridge filters
- Carbon filters
- UV treatment equipment
- Irrigation filters
A filter's micron rating describes the approximate size of particles it is designed to capture. A smaller micron rating generally means finer filtration, but it can also create more resistance and require more maintenance.
Filtration requirements should be chosen for the intended water use, not simply added until the system has many filters.
For drinking-water applications, a pump and filter are only parts of a larger treatment system. A single filter, UV unit, purifier, meter, or home test cannot by itself confirm that roof-collected rainwater is safe to drink.
Plan for Freezing Weather
If the pump, filter, pipe, or pressure tank will be exposed to freezing temperatures, the installation needs a freeze plan.
Water trapped in equipment can expand when frozen and damage:
- Pump housings
- Filters
- Valves
- Pipes
- Pressure gauges
- Fittings
Possible system designs include draining exposed equipment during winter or placing suitable components in protected locations.
Do not assume insulation alone guarantees freeze protection.
Follow the equipment manufacturer's storage and winterizing instructions.
Avoid Choosing a Pump That Is Too Large
More pump power does not automatically make a better system.
An oversized pump can create:
- Excessive pressure
- Frequent cycling
- Higher electrical demand
- More noise
- Greater stress on fittings
- Poor performance with small irrigation zones
It may also require additional controls to make the system behave properly.
Choose a pump that operates comfortably within the flow and pressure range you actually need.
Avoid Choosing a Pump That Is Too Small
An undersized pump may run continuously without reaching the pressure or flow your system needs.
You may notice:
- Weak sprinkler performance
- Slow tank filling
- Poor flow at the end of long pipes
- Pressure dropping when another outlet opens
- The pump running for long periods
Check whether the problem is truly pump size before replacing it. Clogged filters, undersized pipe, suction leaks, blocked screens, low tank levels, and excessive elevation can cause similar symptoms.
A Simple Pump-Sizing Process
You can narrow down your choices by working through the system in order.
1. Identify the water use
Decide whether the pump will supply irrigation, tank transfer, outdoor washing, approved household reuse, or another application.
2. Estimate required flow
Determine how much water the connected equipment needs when operating.
If several outlets will run together, include their combined demand.
3. Determine required pressure
Check the pressure needs of sprinklers, irrigation devices, fixtures, filters, or other equipment.
4. Measure elevation
Determine how far the water must travel vertically from the source water level to the highest outlet.
5. Account for pipe losses
Include long runs, small pipe, elbows, valves, filters, and other restrictions.
6. Check the pump curve
Find a pump that provides the needed flow at your estimated operating head.
7. Check the power supply
Confirm that your electrical, battery, generator, or solar system can properly power the pump and its controls.
8. Confirm connections
Make sure the pump can be connected to the tank and distribution pipes without creating severe restrictions.
9. Add pump protection
Plan for dry-run protection, screening, pressure control, and freezing conditions when relevant.
This approach is much more reliable than choosing a pump by horsepower or maximum GPM alone.
When a Simple DIY Pump Setup Makes Sense
A basic pump installation may be manageable when you are supplying something simple, such as a garden hose from a rainwater tank.
The job becomes more complicated when the system includes:
- Several irrigation zones
- Long pipe runs
- Major elevation changes
- Large pressure requirements
- Household plumbing
- Automatic controls
- Variable-speed equipment
- Complex filtration
- Drinking-water treatment
- Permanent electrical wiring
At that point, proper hydraulic, electrical, plumbing, and treatment design becomes more important.
A qualified pump installer, plumber, electrician, irrigation professional, or water-treatment professional may be appropriate depending on the system.
Frequently Asked Questions
How many gallons per minute should my rainwater pump provide?
It depends on what will run at the same time. Add the flow needed by the outlets or irrigation equipment that may operate together. Then confirm that the pump can provide that flow at your system's actual head, not only at its advertised maximum flow.
Is a submersible pump better than an external pump?
Neither type is always better. Submersible pumps are often quiet and avoid many suction problems because they sit in the water. External pumps are easier to reach for inspection and service. The better choice depends on your tank, installation space, required flow, and maintenance needs.
Can I use a garden pump with an IBC tote?
Often, but the connections and system layout must match. Check the tote outlet, pump inlet, pipe size, required flow, and suction conditions. Avoid restricting a pump with unnecessarily small hoses or adapters.
Can a pump run sprinklers from a rain barrel?
Possibly, but many rain barrels hold relatively little water, while sprinklers can use water quickly. The pump must also provide the sprinkler's required flow and pressure. Check both pump performance and available stored water before setting up the system.
Do I need a pressure tank with my rainwater pump?
Not always. A transfer pump may not need one. Some automatic pressure systems use electronic controls instead. A pressure tank can help reduce pump cycling in certain systems, especially when demand changes frequently.
What happens if my pump is too powerful?
An oversized pump can produce excessive pressure, increase electrical demand, and cycle too often when water demand is small. It may also put unnecessary stress on filters, tubing, fittings, and irrigation equipment.
Should the pump go before or after the filter?
It depends on the type of filter and system. Pumps commonly have screening or coarse filtration before the inlet to protect them from debris, while finer filters may be installed after the pump. Always check the pump and filter manufacturers' installation requirements because some filters are not designed for suction-side use.
Can a rainwater pump make collected water safe to drink?
No. A pump only moves water. It does not establish that rainwater is potable. Potable means suitable for drinking. Drinking-water use requires a properly designed collection and treatment system, suitable maintenance, current laboratory testing, and compliance with applicable local requirements.
