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Which Is the Best Water Pump to Buy?
The best water pump is the one that can deliver the flow and pressure your system needs without being oversized.
For most rainwater systems, that means choosing the pump only after you know:
- What the water will be used for
- How many gallons per minute you need
- How high and how far the pump must move the water
- How much pressure the equipment needs
- Whether the pump will sit above or inside the tank
- What power supply is available
- Whether the pump may ever run dry
A larger horsepower number does not automatically mean a better pump. An oversized pump can cost more to run, cycle too often, stress fittings, and provide more pressure than your system needs.
Start With What the Pump Needs to Do
The right pump for a rain barrel may be very different from the right pump for a buried cistern.
Garden watering
For a hose, drip irrigation, or a small garden line, a modest pump may be enough.
The main questions are:
- How many emitters or sprinklers will run at once?
- What pressure do they need?
- How far is the garden from the tank?
- Is there much elevation change?
Drip irrigation often needs less pressure than sprinklers. Too much pressure may require a pressure regulator.
Rain barrels
Many rain barrels work by gravity alone if the watering point is lower than the barrel.
A pump becomes useful when you want:
- Better hose pressure
- Water moved uphill
- A sprinkler
- Water delivered over a long distance
Small surface pumps are often practical for this type of system.
IBC totes and above-ground tanks
A pump connected near the bottom outlet of an IBC tote or storage tank can usually receive water by gravity.
This makes a surface pump easier to use because the inlet may stay flooded.
Make sure the tank outlet, hose, valves, and pump inlet are large enough to supply the pump. A powerful pump connected through a restrictive fitting may not receive enough water.
Large cisterns
A submersible pump is often a good fit for a large cistern, especially when the tank is below ground.
A submersible pump sits in the water and pushes water toward the point of use. This avoids many of the priming problems that can affect pumps located above the water level.
Household rainwater reuse
Water used for toilets, washing machines, or other household fixtures usually needs a more carefully designed pressure system.
The pump may need:
- A pressure tank or suitable pump controller
- Dry-run protection
- Backflow protection
- Correct plumbing separation
- Filtration appropriate to the intended use
Local plumbing rules may apply.
If rainwater will be used for drinking, the pump is only one part of the system. Roof runoff should not be assumed potable. Drinking-water use requires suitable collection, treatment, current water testing, regular maintenance, and compliance with applicable local requirements.
Compare the Main Types of Water Pumps
| Pump type | Often useful for | Main consideration |
|---|---|---|
| Surface pump | Rain barrels, IBC totes, above-ground tanks, irrigation | Must be able to draw water reliably |
| Submersible pump | Cisterns and deeper tanks | Installed inside the stored water |
| Jet pump | Systems requiring suction lift and household-style pressure | Installation and priming must be correct |
| Booster pump | Increasing pressure in an existing water line | Needs adequate water supplied to its inlet |
| Transfer pump | Moving water from one tank or location to another | Usually selected for flow rather than household pressure |
There is no single type that is best for every system.
Flow Rate Is More Important Than Horsepower Alone
Flow rate tells you how much water a pump can move during a given amount of time. It is commonly shown in gallons per minute, or GPM.
Suppose your irrigation system needs 8 GPM.
A pump that can produce 20 GPM under ideal conditions is not necessarily better. What matters is whether it can provide about 8 GPM at the pressure and elevation your system actually requires.
Pump flow decreases as the pump has to work against greater resistance.
That is why you should not choose a pump from its maximum flow number alone.
Understand Head Height
Head height describes how much resistance the pump must overcome to move water.
Vertical lift is an important part of it.
For example, moving water from a cistern to a garden 20 feet higher requires more work than moving the same water across level ground.
But total head also includes resistance from:
- Long pipes
- Small pipes
- Elbows
- Valves
- Filters
- Irrigation equipment
- Other fittings
Pump manufacturers normally provide a pump curve showing how much water the pump can supply at different head levels.
The useful operating point is where your required flow and system head meet on that curve.
Do Not Buy Based on Maximum Head
A pump may advertise an impressive maximum head.
That number usually represents the point where water flow approaches zero.
It does not mean the pump will provide useful irrigation flow at that height.
For sizing, look at how much flow the pump produces at the head your system actually creates.
Decide How Much Pressure You Need
Pressure is especially important for:
- Sprinklers
- Household fixtures
- Some irrigation valves
- Certain filtration equipment
Pressure is often measured in pounds per square inch, or PSI.
Different equipment has different requirements, so check the operating requirements of the equipment the pump must supply.
Avoid assuming that more pressure is better.
Excess pressure can damage or shorten the life of hoses, irrigation parts, filters, fittings, and other components.
Check the Suction Side Carefully
Surface pumps have an important limitation: they must pull water into the pump before they can push it onward.
Suction problems are a common cause of poor pump performance.
Potential problems include:
- Air leaking into the suction line
- A suction hose that is too small
- Excessive suction lift
- A blocked screen
- A clogged filter
- Too many fittings
- A pump that has lost its prime
Whenever possible, placing a surface pump below the normal water level of an above-ground tank can simplify the setup because water can flow toward the pump by gravity.
When a Submersible Pump Makes More Sense
A submersible pump is often worth considering when the storage tank is deep or below ground.
Because the pump is already underwater, it does not need to lift water through a suction pipe before pumping begins.
This can reduce priming problems.
However, installation and maintenance may be less convenient because the pump must be removed from the tank for some repairs.
Any electrical equipment used around stored water must be installed according to its instructions and applicable electrical requirements. Use suitable outdoor and wet-location electrical protection where required. Have a qualified electrician handle work that is beyond basic plug-in equipment.
Look for Dry-Run Protection
A water pump can be damaged if it operates without enough water.
This matters in rainwater systems because storage levels naturally rise and fall.
Dry-run protection can stop the pump when the tank gets too low.
Depending on the system, protection may come from:
- A float switch
- A level sensor
- A pump controller
- A pump with built-in protection
The exact setup should match the pump manufacturer's requirements.
Do not rely only on remembering to turn the pump off.
Check Your Tank Connections
The pump cannot move water faster than the tank and plumbing can supply it.
Planning around matching a water pump to system demand helps understand allowable run time under normal household demand.
Before buying a pump, check:
- Tank outlet size
- Bulkhead fitting size
- Valve size
- Suction hose or pipe diameter
- Pump inlet size
- Pump outlet size
A bulkhead fitting is a fitting that passes through the wall of a tank and creates a sealed connection.
Reducing a large pump inlet immediately to a much smaller tank outlet can restrict water flow and contribute to poor performance.
Follow the pump manufacturer's minimum inlet-pipe recommendations.
Consider Automatic Versus Manual Operation
A simple transfer pump may only need an on/off switch.
Other systems are easier to use with automatic controls.
An automatic pressure system can start the pump when a valve or faucet opens and stop it when water use ends.
Depending on the pump design, this may involve:
- A pressure switch
- A pressure tank
- An electronic pump controller
- A variable-speed controller
Frequent starting and stopping is called short cycling. It can shorten pump life.
A correctly sized pressure tank or suitable controller can help reduce excessive cycling where the pump design calls for one.
Match the Pump to Your Power Supply
Check the available power before choosing a pump.
Possible systems include:
- Standard household electricity
- Dedicated higher-voltage circuits
- Solar-powered systems
- Battery-based systems
- Generator-backed systems
Do not choose a pump based only on horsepower.
Check the actual electrical requirements, including starting demand where applicable.
A pump that works easily on utility power may be a poor match for a small off-grid electrical system.
Think About Noise and Location
Surface pumps create more noticeable noise because the motor is outside the tank.
If the pump will be near a house, patio, cabin, or bedroom, pump location can matter.
Submersible pumps are usually quieter from outside the tank because the pump is surrounded by water.
Any surface pump should also have suitable weather protection and enough ventilation according to its installation instructions.
Protect the Pump From Debris
Rainwater can carry:
- Leaves
- Roof grit
- Sediment
- Insects
- Organic material
A pump inlet should be protected from debris that could block or damage the pump.
A rainwater collection system may include gutter screens, prefiltration, a first-flush device, tank inlet screening, or pump intake protection depending on the setup.
A first flush device diverts some of the early roof runoff from a rain event. That early runoff may contain more debris and contamination washed from the roof.
Do not install extremely fine filtration on the pump inlet unless the pump and system are designed for it. A badly restricted suction line can cause pump problems.
Consider Freezing Weather
If the pump, pipes, valves, or filters are exposed to freezing temperatures, winter conditions must be part of the design.
A pump that holds water can be damaged if that water freezes and expands.
Depending on the installation, winter preparation may involve draining exposed equipment, relocating components, or using a system specifically designed for the conditions.
Do not assume insulation alone guarantees freeze protection.
What Size Water Pump Should You Buy?
A useful selection process is:
- Calculate the required flow. Add the flow of everything that may operate at the same time.
- Determine the vertical lift. Measure the elevation difference between the water source and the point of use.
- Account for plumbing resistance. Long or narrow piping and many fittings increase resistance.
- Determine required pressure. Check the requirements of sprinklers, fixtures, filters, or other equipment.
- Check the pump curve. Confirm that the pump can provide the required flow at your expected total head.
- Check the inlet requirements. Make sure the tank outlet and suction plumbing can supply the pump.
- Choose suitable controls and protection. Consider dry-run protection, pressure controls, and appropriate electrical protection.
This approach is more reliable than deciding between pumps only by horsepower.
Is a 1 HP Pump Better Than a 1/2 HP Pump?
Not necessarily.
Horsepower describes motor power. It does not directly tell you how much useful water the pump will deliver in your installation.
Two pumps with the same horsepower can have very different flow and head characteristics.
A smaller pump operating near the middle of its intended range may be a better choice than a larger pump that constantly starts and stops.
Always compare pump curves and system requirements.
Features Worth Looking For
Rather than looking for the pump with the longest feature list, prioritize features that solve real problems in your system.
Useful features may include:
- Dry-run protection
- Thermal overload protection
- Suitable automatic controls
- Accessible service parts
- Connections that match your plumbing
- A pump curve that covers your required operating point
- Materials suitable for the intended water use
- Weather protection appropriate to the installation
For a submerged pump, also confirm that it is specifically designed for submersible use.
When to Get Professional Help
A simple plug-in pump connected to a garden tank can often be a manageable DIY project.
Professional help becomes more important when the system involves:
- Household plumbing
- High pressure
- Permanent electrical wiring
- Buried cisterns
- Complex pump controls
- Large pressure tanks
- Drinking-water treatment
- Backflow prevention
- Significant excavation
- Difficult freeze protection
A pump installer, plumber, irrigation professional, or electrician can also help calculate total dynamic head for a system where the pipe layout is complicated.
The Best Choice for Most Rainwater Systems
For a small above-ground rainwater tank used for garden watering, a properly sized surface pump is often the simplest option.
For a large or buried cistern, a properly sized submersible pump often makes more sense.
For household reuse, choose the pump as part of the complete pressure, plumbing, filtration, control, and water-quality system rather than as a stand-alone device.
In every case, buy based on required flow at the actual operating head, not maximum horsepower or maximum advertised flow.
Frequently Asked Questions
What is the best type of water pump for a rainwater tank?
A surface pump often works well with an above-ground rainwater tank, especially when the pump receives water from a low tank outlet. A submersible pump may be more suitable for a deep or buried cistern.
How many horsepower should my water pump have?
There is no standard horsepower that is best for every rainwater system. Determine the required flow, head, and pressure first. Then choose a pump whose performance curve meets those requirements.
Is a bigger water pump always better?
No. An oversized pump can create unnecessary pressure, frequent cycling, higher electrical demand, and harder-to-control flow. Proper sizing is usually better than simply choosing the largest pump.
What does maximum head mean on a water pump?
Maximum head is approximately the greatest height or resistance a pump can overcome before useful flow falls to nearly zero. It should not be confused with the pump's normal working range.
Should I buy a submersible or external pump?
Choose a surface or external pump when the tank layout provides reliable water to the pump inlet and easy access is important. Consider a submersible pump when the water is stored well below the point where an external pump would sit or when avoiding suction and priming problems is important.
Does a rainwater pump need a pressure tank?
Not every system does. Simple irrigation or transfer systems may not need one. Some automatic pressure systems use a pressure tank to maintain pressure and reduce pump cycling. Follow the requirements of the specific pump and control system.
Can I pump rainwater directly into my house?
Rainwater can be used for certain household purposes where local rules allow it, but the system may require proper plumbing separation, backflow protection, treatment, controls, and other safeguards. Rainwater should not be assumed safe to drink simply because it has been pumped or filtered.
What should I check before buying a pump?
Check your required flow, elevation change, pipe length, pressure requirement, tank outlet size, pump location, power supply, controls, dry-run protection, climate conditions, and the manufacturer's pump curve.
