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A rainwater tank does not create enough pressure for many sprinklers, long hose runs, or household fixtures on its own. A pump solves that problem by drawing water from the tank and pushing it through the delivery line.
For most systems, the basic arrangement is:
Rainwater tank → shutoff valve → coarse strainer → pump → check valve or pump controls → pressure system or irrigation line
The exact layout depends on the pump type and how you plan to use the water. Garden watering can be simple. Supplying toilets, laundry, or other household fixtures needs more controls and careful separation from drinking-water plumbing.
Decide What the Pump Will Supply
Start with the water use rather than the pump.
A small garden system may only need enough flow and pressure for:
- A garden hose
- Drip irrigation
- A small sprinkler
- Hand watering
A larger system may supply:
- Several irrigation zones
- Toilets
- Laundry
- Outdoor faucets
- A cabin or other building
These uses require different amounts of flow rate and pressure.
Flow rate is how much water the pump moves in a certain amount of time, usually gallons per minute or liters per minute. Pressure determines how strongly that water can move through pipes, hoses, valves, filters, and fixtures.
The pump must provide enough of both at the same time.
Choose Between a Surface Pump and a Submersible Pump
Rainwater systems commonly use either a surface pump or a submersible pump.
Surface Pump
A surface pump sits outside the tank and pulls water through a suction pipe.
A typical layout looks like this:
Tank outlet → shutoff valve → suction strainer → pump → delivery pipe
Surface pumps are convenient because you can reach them easily for inspection and maintenance.
Whenever possible, position the pump lower than the normal water level in the tank. This creates a flooded suction, meaning water naturally fills the suction pipe instead of the pump having to lift it.
A flooded suction arrangement usually makes priming easier and reduces suction problems.
Submersible Pump
A submersible pump sits inside the rainwater tank.
Its layout is closer to:
Submersible pump → discharge pipe → tank outlet or lid connection → check valve/controls → delivery system
Because the pump is already underwater, it does not normally need the same suction-line priming as an external pump.
Submersible pumps can also avoid some of the suction problems that occur when a surface pump is located above the tank water level.
However, servicing the pump usually means opening the tank and retrieving it. Do not enter a cistern or enclosed tank to reach a pump. Confined-space entry can be dangerous and should be left to properly trained professionals.
Check the Pump Connections Before Buying Fittings
Do not assume the tank outlet, pump inlet, and hose will connect directly.
Check:
- Tank outlet size
- Pump inlet size
- Pump discharge size
- Pipe or hose size
- Thread type
- Male or female threads
- Whether the connection requires an adapter
- Whether the pump manufacturer permits flexible hose on the suction side
A rainwater tank may have a threaded outlet or a bulkhead fitting.
A bulkhead fitting is a fitting that passes through the tank wall while creating a sealed connection. Many tanks and IBC totes already have a bottom outlet that can be adapted to the pump plumbing.
Avoid reducing the suction pipe unnecessarily. A narrow suction line can restrict flow and make it harder for a surface pump to draw water.
Follow the pump manufacturer's required suction-pipe diameter rather than simply matching whatever garden hose happens to be available.
A Basic Surface-Pump Connection
For a simple garden or irrigation system, the setup may look like this:
Tank → tank valve → full-flow isolation valve → coarse strainer → pump → check valve if required → hose or irrigation system
Some pumps already contain check valves or other controls, so always check the manufacturer's installation instructions before adding another one.
1. Install the Pump on a Firm Base
Place the pump on a stable, level surface.
Keep it:
- Out of standing water
- Protected from flooding
- Protected from direct weather unless rated for outdoor exposure
- Accessible for maintenance
- Close to the tank when practical
Short suction piping is generally better than a long, complicated route.
Avoid unnecessary elbows, reducers, and fittings between the tank and a surface pump.
2. Use the Tank's Low Outlet When Suitable
A low tank outlet is useful for a surface pump because the stored water can naturally flow toward the pump.
Install a shutoff valve between the tank and pump.
The valve lets you isolate the tank when servicing:
- The pump
- The strainer
- Pipe connections
- Valves
Without an isolation valve, repairing the pump may require draining much of the tank.
Do not permanently block the tank's overflow. The tank still needs a safe way to discharge excess rainwater.
3. Add a Coarse Strainer Before the Pump
Roof runoff can contain leaves, grit, insects, sediment, and other debris.
A coarse strainer before the pump can help keep larger material out of the pump.
This is different from a fine drinking-water filter.
Avoid placing an unnecessarily restrictive fine filter in a surface pump's suction line. A dirty or undersized filter can starve the pump of water and cause poor performance.
Fine filtration is often easier to manage on the discharge side, depending on the pump and intended use.
4. Connect the Suction Pipe
Connect the tank outlet to the pump inlet using pipe and fittings suitable for the system.
The suction side must be airtight.
A fitting can appear watertight while still allowing air to enter when the pump operates. Even a small suction-side air leak can cause:
- Loss of prime
- Surging flow
- Low pressure
- Excessive pump noise
- Difficulty starting the pump
Support the pipe so its weight does not hang from the tank fitting or pump housing.
A suitable flexible connector may help isolate vibration when the pump manufacturer permits one.
5. Connect the Pump Discharge
Connect the pump outlet to the line supplying the garden, irrigation system, or pressure system.
This side of the pump operates under pressure, so all pipe, hose, valves, fittings, and filters must be suitable for the pressure the pump can produce.
A simple hose-watering system may connect fairly directly to the pump.
An automatic household or irrigation system usually needs additional controls.
When You Need a Check Valve
A check valve allows water to move in one direction while helping prevent it from flowing backward.
Whether you need one depends on the pump.
A surface pump located above the tank water level may use a foot valve or check valve to help keep its suction line full after priming.
Some pumps already have an internal check valve.
Some submersible pumps also require or include one on their discharge.
Adding valves without understanding the pump can cause other problems, so follow its installation requirements.
Prime a Surface Pump Before Starting It
Many surface centrifugal pumps cannot pump air effectively. Their pump housing and suction piping need to contain water before the pump starts.
This process is called priming.
Follow the manufacturer's priming procedure. Typically, this involves filling the appropriate pump chamber and suction line with water before starting the unit.
Never assume a pump is self-priming just because it is connected to a full tank.
A pump that runs without enough water can overheat or damage internal seals and components.
If a correctly primed pump repeatedly loses its prime, check for:
- Suction-side air leaks
- A leaking check or foot valve
- Loose threaded connections
- Excessive suction lift
- A blocked strainer
- An empty tank
- Incorrect pipe sizing
Understand Suction Lift and Head Height
Two measurements matter when positioning and selecting a pump.
Suction Lift
Suction lift applies mainly when a surface pump sits higher than the water level.
It is the vertical distance the pump must lift water before it reaches the pump inlet.
The greater the lift, the harder the pump has to work. Long suction pipes, small pipe diameters, filters, elbows, and valves add further resistance.
Do not choose a pump based only on its advertised maximum suction lift. Maximum ratings do not represent an ideal everyday operating condition.
Head Height
Head height describes the resistance the pump must overcome while moving water.
It includes more than just elevation.
A real system may have resistance from:
- Vertical elevation
- Pipe length
- Elbows
- Valves
- Filters
- Irrigation equipment
- Required outlet pressure
This combined resistance is often called total dynamic head.
Examine pump choices for different delivery conditions to understand suction lift and safeguards against dry running.
For water, approximately 2.31 feet of head corresponds to 1 psi of pressure. A pump's flow normally falls as the required head increases.
That is why a pump advertised for a high maximum flow may deliver much less water once it is pushing water uphill and through a real plumbing system.
Add Pressure Controls for Automatic Water Supply
You do not necessarily need a pressure tank just to run a hose from a manually switched pump.
For household fixtures or an automatic irrigation system, pressure controls become much more useful.
A common arrangement is:
Rainwater tank → pump → check valve → pressure tank → pressure switch/control → distribution plumbing
A pressure tank stores a small amount of pressurized water. This can reduce how often the pump starts every time a small amount of water is used.
A pressure switch turns the pump on and off at set pressures.
Some modern pump systems use an electronic pressure controller instead of a traditional pressure tank and pressure switch arrangement.
Follow the specific pump manufacturer's design. Pumps vary in how they handle automatic starting, minimum flow, pressure tanks, check valves, and dry-run protection.
Install Dry-Run Protection
A rainwater tank eventually becomes empty if water use exceeds rainfall.
That makes dry-run protection especially useful.
Dry-run protection stops the pump when there is not enough water available.
Depending on the system, this may use:
- A float switch
- A tank-level sensor
- Electronic pump protection
- A controller built into the pump
Without suitable protection, an unattended pump may continue trying to operate after the tank is empty.
Place level controls so normal sediment accumulation at the bottom of the tank does not interfere with them.
Avoid Pumping the Dirtiest Water From the Tank Bottom
Sediment tends to collect at the bottom of a rainwater tank.
Connecting a pump directly to the lowest point can make maintenance easy, but it may also put the pump close to settled debris.
The best approach depends on the tank.
Options can include:
- Drawing from an outlet slightly above the tank floor
- Using a suitable internal pickup
- Using a floating intake with some systems
- Keeping the tank clean enough that heavy sediment does not accumulate
A floating intake draws water from below the surface rather than directly from the sediment layer at the bottom.
Not every pump or tank needs one.
Good roof screening, gutter maintenance, and suitable prefiltration can also reduce the amount of debris reaching the tank.
Put Fine Filters After the Pump When Appropriate
A pump is only one part of the system.
For irrigation, you may need a filter fine enough to protect:
- Drip emitters
- Small sprinkler nozzles
- Irrigation valves
The required micron rating depends on the equipment being protected.
A micron rating describes the approximate size of particles a filter is designed to capture. A lower micron number means finer filtration.
Fine filters create resistance, especially as they become dirty. Include their pressure loss when deciding whether the pump can provide enough flow and pressure.
Install filters where they can be reached easily for cleaning or replacement.
Protect the Pump From Freezing
Water trapped inside a pump, filter housing, valve, or exposed pipe can freeze and expand.
In freezing climates, plan for winter before permanently plumbing the system.
Depending on the installation, this may mean:
- Draining exposed equipment
- Providing suitable freeze protection
- Installing drain points
- Placing equipment within a protected space
- Removing seasonal pumps when appropriate
Do not assume insulation alone will prevent freezing.
Follow the manufacturer's cold-weather storage and winterization requirements.
Keep Electrical Work Safe
Water and electricity require extra care.
Outdoor pumps should use electrical equipment suitable for the location and should have the shock protection required by applicable electrical rules. Do not run permanent pumps from improvised extension-cord arrangements.
Keep electrical connections away from standing water and locations where the tank may overflow.
If the installation requires new outdoor circuits, hard wiring, buried electrical cable, control panels, or changes to household wiring, use a qualified electrician.
Do Not Connect Rainwater Directly to Drinking-Water Plumbing
Rainwater collected from a roof is not automatically safe to drink. It can contain microorganisms and chemicals picked up from the air, roofing materials, gutters, pipes, storage equipment, and animal waste. The CDC recommends matching water quality to its intended use and using appropriate testing and treatment when rainwater is used for drinking, cooking, or bathing.
Potable means water suitable for drinking. Non-potable water is water that is not intended to meet drinking-water requirements.
A pumped rainwater system should not simply be connected to a home's potable water system. A connection between potable and non-potable plumbing can create a cross-connection, allowing contaminated water to move backward into drinking-water piping under some pressure conditions. EPA guidance treats cross-connections and backflow as water-quality hazards.
If a building will have both utility water and pumped rainwater, the plumbing arrangement, backflow protection, labeling, and permitted uses should meet current local requirements. Use a qualified plumber or rainwater-system professional where the two systems could interact.
For drinking-water use, adding a pump and a single filter does not make stored roof runoff potable. Treat drinking water as a complete system involving suitable collection materials, debris control, treatment selected for the actual contaminants, current laboratory testing, maintenance, and applicable health and plumbing requirements.
A Practical Pump Layout for Garden Watering
A simple garden setup might be:
Roof → gutter screen → rainwater tank → tank outlet → shutoff valve → coarse pump strainer → surface pump → irrigation filter → garden hose or irrigation line
If the pump sits below the tank's water level, the suction side can remain flooded.
For an automatic system, add the controls required by the pump, such as:
Tank → pump → check/control arrangement → pressure tank or electronic controller → filter → irrigation system
A submersible version could be:
Tank → submersible pump → discharge pipe → check/control arrangement → filter → irrigation system
The pump manufacturer's required arrangement takes priority over a generic layout.
Common Problems After Connecting the Pump
Pump Runs but No Water Comes Out
Check:
- Tank water level
- Pump priming
- Closed valves
- Blocked strainers
- Suction-side air leaks
- Incorrect check-valve direction
Stop the pump if it is not receiving water rather than allowing it to run continuously.
Pump Has Weak Flow
Possible causes include:
- Suction pipe that is too small
- Long suction runs
- Dirty strainers
- Clogged filters
- Excessive elevation
- Too many restrictions
- Low tank level
- A pump that is too small for the system
Remember that pump performance must be evaluated at the actual head the system creates, not just at the pump's maximum-flow rating.
Pump Keeps Turning On and Off
Rapid cycling can occur when:
- A pressure tank is too small
- A pressure tank is incorrectly charged
- There is a plumbing leak
- A check valve leaks
- An automatic controller is unsuitable for the application
- The system flow is below what the pump controller expects
Repeated rapid cycling can shorten pump life, so correct the cause instead of treating it as normal operation.
Pump Loses Prime
Look closely at the suction side.
A loose threaded connection, leaking foot valve, damaged seal, or tiny air leak may allow the suction pipe to drain between uses.
Pump Is Very Noisy
Noise can come from:
- Air entering the suction line
- Restricted water supply
- Cavitation
- Loose mounting
- Pipe vibration
- Worn pump components
Cavitation happens when conditions at the pump inlet cause vapor bubbles to form and collapse. Persistent cavitation can damage a pump. If improving the suction arrangement does not solve the problem, stop using the pump and have the installation checked.
Before Switching the Pump On
Run through a final check:
- The tank contains enough water.
- The tank outlet valve is open.
- Suction fittings are airtight.
- The suction pipe meets the pump's size requirements.
- The strainer is clean.
- The pump is securely mounted.
- The discharge valve arrangement is correct.
- Any required check valve faces the right direction.
- A surface pump has been primed as required.
- Dry-run protection is operating.
- Filters and pipes are pressure-rated for the system.
- Electrical connections are suitable for the location.
- The rainwater plumbing cannot contaminate potable plumbing.
Then start the pump according to its manual and check every connection for leaks.
Watch the system during its first full operating cycle. Confirm that the pump starts normally, maintains useful flow, reaches the expected pressure, and shuts down correctly if automatic controls are installed.
Frequently Asked Questions
Can I connect a garden hose directly from a rainwater tank to a pump?
Yes, in some simple systems, but the hose must be suitable for the pump's suction requirements. Many ordinary garden hoses are not ideal suction lines because they may be too small, restrictive, or able to collapse under suction. Use the pipe or reinforced suction hose size recommended by the pump manufacturer.
Should a rainwater pump go before or after the filter?
A coarse strainer is commonly installed before the pump to stop larger debris. Finer filters are often installed after the pump so they do not unnecessarily restrict the suction line. The correct arrangement depends on the pump, filter, and intended water use.
Does a rainwater tank pump need a pressure tank?
Not always. A manually operated garden pump can work without one. Automatic systems supplying faucets, toilets, or irrigation zones may use a pressure tank and pressure switch or an electronic pump controller to control starting and stopping.
Can I put the pump above the rainwater tank?
A surface pump can sometimes sit above the tank water level, but it must then lift water through its suction line. This makes priming, suction lift, air leaks, and pipe resistance more important. Keeping the pump close to the tank and below the water level is usually simpler when the site allows it.
How do I stop a rainwater pump from running when the tank is empty?
Use dry-run protection. Depending on the pump, this may be a float switch, tank-level sensor, electronic controller, or protection built into the pump. Check that the device is compatible with the pump's electrical load and control system.
Can a rainwater pump supply my house?
It can supply suitable household uses if the pump and plumbing system are designed for them, but roof-collected rainwater should not simply be connected to potable plumbing. Household systems may require pressure controls, appropriate treatment, backflow protection, separate plumbing, and compliance with local requirements. Drinking-water use also requires a much more complete water-quality plan.
Do I need a check valve between the rainwater tank and pump?
It depends on the pump and layout. A check or foot valve may be needed to keep a surface pump's suction line primed, while some pumps already contain one. Install only the valve arrangement specified or permitted by the pump manufacturer.
