Winterizing an RO System: If you live in a cold climate or plan to leave your home vacant during the winter, winterizing your reverse osmosis (RO) system can help protect the membrane, filters, storage tank, tubing, fittings, and other components from freezing-related damage.
Water expands when it freezes. In a confined plumbing system, that expansion can put significant stress on housings, connections, tubing, valves, and tanks. A frozen RO system may develop leaks or component damage that isn’t discovered until the system is returned to service.
The good news is that most RO systems installed inside a heated home don’t require extensive winterization. The main concern is preventing the system and its water-filled components from being exposed to freezing temperatures.
For homes that will be vacant, cabins, vacation properties, RVs, garages, or other locations where temperatures can fall below freezing, a more thorough shutdown and drainage procedure may be appropriate.
Related guide: For year-round filter replacement, membrane care, sanitization, tank maintenance, and troubleshooting, see the Reverse Osmosis Maintenance Guide on Revosmo.com.
Table of Contents
- Does an RO System Need to Be Winterized?
- Why Freezing Can Damage an RO System
- What Parts of an RO System Can Freeze?
- When Should You Winterize an RO System?
- How to Winterize an RO System
- Step 1: Turn Off the Water Supply
- Step 2: Drain the RO Storage Tank
- Step 3: Open the RO Faucet
- Step 4: Drain the RO Tubing and Components
- Step 5: Protect the RO Membrane
- Step 6: Protect Filters and Filter Housings
- Step 7: Inspect the System Before Leaving
- How to Winterize a Tankless RO System
- How to Winterize an RO System in a Heated Home
- How to Restart a Winterized RO System
- Should You Replace RO Filters After Winter Storage?
- Common RO Winterization Mistakes
- RO Winterization Checklist
- Winterizing an RO System FAQ
- Final Thoughts
Does an RO System Need to Be Winterized?
Whether you need to winterize your RO system depends primarily on temperature and how long the system will be unused.
An RO system located under a kitchen sink inside a normally heated home generally doesn’t need to be winterized simply because winter is approaching.
If the indoor temperature remains safely above freezing, normal RO maintenance is sufficient.
Winterization becomes much more important when the system is located in an area that could freeze, such as:
- An unheated vacation home
- Cabin
- Garage
- Basement
- Detached guest house
- RV
- Mobile home
- Seasonal property
- Outdoor utility room
- Unheated commercial space
If the property will be vacant for several weeks or months and heat will be turned off, consider winterizing the RO system before temperatures can reach freezing.
EPA guidance for RO membrane maintenance notes that membranes that are not in use should not be allowed to freeze or dry out and should be stored using the manufacturer’s recommended preservation procedure when applicable.
Always follow the specific winterization instructions supplied by your RO manufacturer.
Why Freezing Can Damage an RO System
Water expands as it freezes.
That’s a problem for RO systems because water can remain inside:
- Filter housings
- RO membrane housings
- Tubing
- Storage tanks
- Valves
- Fittings
- Pumps
- Flow restrictors
- Automatic shutoff components
Even if the outside of a component looks intact, freezing water can damage internal seals or create cracks that become apparent when the system is pressurized again.
A freeze-damaged system may not reveal the problem until you turn the water back on.
Potential symptoms include:
- Leaking filter housings
- Cracked fittings
- Split tubing
- Damaged valves
- Storage-tank leaks
- Low water production
- Continuous drain flow
- Reduced water pressure
- Water-quality problems
The risk is especially important for systems installed in spaces that aren’t protected from freezing temperatures.
What Parts of an RO System Can Freeze?
A typical under-sink RO system contains several water-filled components.
| Component | Freeze Risk | What to Do |
| Sediment filter housing | High | Drain if exposed to freezing |
| Carbon filter housings | High | Drain if exposed to freezing |
| RO membrane housing | High | Follow manufacturer’s storage procedure |
| RO tubing | High | Drain where practical |
| Storage tank | High | Drain completely |
| Faucet | Moderate | Drain water from connected tubing |
| Automatic shutoff valve | Moderate | Follow manufacturer instructions |
| Flow restrictor | Moderate | Drain/protect from freezing |
| Permeate pump | System-dependent | Follow manufacturer instructions |
| Booster pump | System-dependent | Follow manufacturer instructions |
The RO membrane deserves special attention. Don’t simply remove a membrane and leave it sitting dry unless the manufacturer specifically says that is acceptable.
For systems that will be stored for an extended period, membrane preservation requirements can vary considerably by membrane type and manufacturer.
When Should You Winterize an RO System?
Winterization should generally be completed before freezing temperatures are expected, rather than after the system has already been exposed to freezing conditions.
Consider winterizing when:
- The property will be vacant.
- Heat will be turned off.
- Indoor temperatures could fall below freezing.
- The RO system is located in an unheated space.
- The system is installed in an RV or seasonal property.
- The property is being closed for the winter.
- You expect prolonged periods of freezing temperatures.
For a normally occupied house with reliable heat, extensive winterization usually isn’t necessary.
However, it’s still a good idea to know where the RO water shutoff valve is located and how to shut down the system in an emergency.
How to Winterize an RO System
The exact procedure varies by RO system.
A basic winterization process typically involves:
- Turn off the RO water supply.
- Shut off the storage tank.
- Drain the storage tank.
- Open the RO faucet.
- Drain accessible water from the system.
- Follow the manufacturer’s membrane-storage procedure.
- Protect or remove filters as instructed.
- Inspect tubing and fittings.
- Leave the system depressurized.
- Protect the system from freezing temperatures.
For a system with a pump, UV stage, remineralization filter, specialty cartridges, or other accessories, follow the manufacturer’s instructions for those components as well.
Step 1: Turn Off the Water Supply
Locate the valve supplying water to the RO system.
It is typically installed on the cold-water line underneath the kitchen sink.
Turn the valve off.
If your system has additional valves, pumps, or controls, follow the manufacturer’s shutdown procedure.
Do not begin disconnecting pressurized components while the system is still under pressure.
Step 2: Drain the RO Storage Tank
If your RO system has a storage tank, drain it before leaving the system unused.
Close the tank valve if necessary and open the RO faucet.
Allow the tank to empty.
This can take several minutes depending on the system and the condition of the tank.
EPA recommends periodically draining residential RO storage tanks as part of normal maintenance and notes that draining the tank also helps the membrane maintain the pressure needed for contaminant removal.
For winterization, however, the goal is more specific: remove as much water as practical from components that could be exposed to freezing temperatures.
Step 3: Open the RO Faucet
After the storage tank has been drained, open the RO faucet.
This relieves pressure in the product-water side of the system and allows additional water to leave the tubing.
Leave the faucet open while draining the system, following your manufacturer’s instructions.
Once water stops flowing, close the faucet if the manufacturer recommends doing so.
Step 4: Drain the RO Tubing and Components
This step becomes particularly important when the system is located somewhere that could freeze.
Depending on the design of your RO system, water may remain inside:
- Filter housings
- Membrane housing
- Product-water tubing
- Drain tubing
- Tank connections
- Post-filter
- Specialty filters
Do not automatically disconnect every tube and fitting.
Quick-connect fittings can be damaged if they are improperly disconnected or reconnected.
Instead, consult the manufacturer’s winterization instructions and drain only the components that the manufacturer identifies as necessary.
Step 5: Protect the RO Membrane
The membrane is one of the most important components to handle correctly during extended storage.
Do not assume that the RO membrane can simply be removed and allowed to dry.
EPA guidance for RO membrane maintenance states that membranes not in use should not be allowed to dry out or freeze and should be stored in the manufacturer’s recommended preservative solution when applicable.
Different membrane manufacturers can specify different storage procedures.
Depending on the system, the recommended procedure may involve:
- Keeping the membrane installed
- Removing the membrane
- Keeping the membrane wet
- Using an approved preservation solution
- Sealing the membrane in an appropriate container
- Replacing the membrane when the system is returned to service
Follow the membrane manufacturer’s instructions rather than improvising a preservation solution.
Step 6: Protect Filters and Filter Housings
Filter cartridges and housings can also retain water.
If freezing temperatures are possible, consult your manufacturer’s instructions for whether cartridges should be removed.
Depending on the system, you may be instructed to:
- Remove cartridges
- Drain housings
- Leave cartridges installed
- Replace cartridges after storage
- Sanitize the system before restarting
Don’t assume that a filter cartridge that survived freezing is automatically suitable for continued use.
Freezing can potentially affect the cartridge, housing or seals.
If you’re uncertain about the condition of a cartridge after freezing, replacement is generally preferable to taking unnecessary chances with drinking-water equipment.
Step 7: Inspect the System Before Leaving
Before leaving the property, perform a visual inspection.
Look for:
- Water around filter housings
- Cracked plastic
- Damaged tubing
- Loose fittings
- Corroded components
- Damaged valves
- Tank leaks
- Signs of previous leakage
Make sure the incoming RO supply is shut off.
If the system includes electrical components such as a booster pump, UV system or electronic controls, follow the manufacturer’s shutdown instructions for those components as well.
How to Winterize a Tankless RO System
Tankless RO systems don’t have a large pressurized storage tank, but they still contain water in their:
- Filter cartridges
- Membrane housing
- Tubing
- Pumps
- Valves
- Flow-control components
The absence of a storage tank does not make a tankless system immune to freezing.
For a tankless system:
- Shut off the incoming water.
- Disconnect power if instructed by the manufacturer.
- Open the RO faucet to relieve pressure.
- Drain the system according to the manufacturer’s procedure.
- Address the membrane according to its storage requirements.
- Protect the unit and tubing from freezing.
- Follow the manufacturer’s startup procedure when returning the system to service.
Some modern tankless RO systems have proprietary components and electronic controls, so manufacturer-specific instructions are particularly important.
How to Winterize an RO System in a Heated Home
If your RO system is installed inside a heated home and the indoor temperature will remain comfortably above freezing, you usually don’t need to completely drain the system.
Instead, focus on normal maintenance.
Before winter:
- Check filter replacement dates.
- Inspect tubing and connections.
- Check for leaks.
- Verify the storage tank is functioning properly.
- Replace overdue filters.
- Sanitize the system if due.
- Check the RO faucet.
- Confirm the incoming water shutoff valve works.
EPA recommends replacing RO filters and membranes according to the manufacturer’s maintenance instructions. As a general reference, EPA says many systems require prefilter replacement about every six months and membrane replacement about every one to five years, depending on water quality and use.
A heated home provides the primary protection against freezing; winterization in this situation is mostly about preventive maintenance and emergency preparedness.
How to Restart a Winterized RO System
Don’t simply turn the water back on and immediately start drinking from the faucet.
A proper restart procedure should include an inspection and flushing process.
1. Inspect the System
Check:
- Filter housings
- Tubing
- Fittings
- Storage tank
- Faucet
- Valves
- Pumps
- Electrical components
Look for cracks, leaks or other signs of damage.
2. Reinstall Components
If you removed filters or the membrane for winter storage, reinstall them according to the manufacturer’s instructions.
Make sure every connection is properly seated.
3. Turn the Water Supply Back On Slowly
Open the supply valve gradually.
Watch the system carefully for leaks.
Don’t leave the system unattended during the initial pressurization.
4. Check for Leaks
Inspect every connection.
Pay particular attention to filter housings and quick-connect fittings.
If you see water leaking, shut the system down immediately and determine the cause before continuing.
5. Flush the System
Follow the manufacturer’s startup and flushing instructions.
Depending on the system and what was removed during winterization, you may need to discard one or more tanks of water.
6. Replace Filters if Necessary
If filters were stored for an extended period or the manufacturer recommends replacing them after seasonal shutdown, install fresh cartridges.
7. Consider Sanitization
If the system was shut down for an extended period, sanitization may be appropriate before returning it to normal drinking-water service.
The correct sanitization procedure varies by system, so follow the manufacturer’s instructions.
EPA notes that many manufacturers recommend annual sanitization of RO storage tanks.
Should You Replace RO Filters After Winter Storage?
Not necessarily.
The answer depends on:
- How long the system was stored
- Whether the filters remained installed
- Whether they were exposed to freezing temperatures
- Manufacturer recommendations
- Filter age
- Whether the system was sanitized
- Whether the system develops an unusual taste or odor after startup
If the system was properly drained and stored in accordance with the manufacturer’s instructions, existing filters may still be usable.
However, if filters were exposed to freezing conditions or have reached the end of their normal service life, replacing them is a sensible maintenance step.
If the system develops an unexpected taste or odor after being restarted, EPA recommends considering maintenance because changes in taste or odor can indicate that filters or other system components require attention.
Common RO Winterization Mistakes
Mistake 1: Assuming an indoor RO system is automatically protected
An RO system located inside a garage, basement or cabin may still freeze.
The location of the system matters more than the fact that it is technically “indoors.”
Mistake 2: Leaving the storage tank full
A full tank contains a significant amount of water that can freeze.
If the property could experience freezing temperatures, follow the manufacturer’s procedure for draining the tank.
Mistake 3: Forgetting the tubing
Draining the tank doesn’t necessarily drain all of the water in the system.
Tubing and filter housings can still contain water.
Mistake 4: Letting the membrane freeze
Freezing can damage an RO membrane.
Follow the membrane manufacturer’s storage requirements.
Mistake 5: Allowing the membrane to dry out
For systems requiring wet storage, allowing the membrane to dry can damage it or affect its performance.
Follow the manufacturer’s storage instructions.
Mistake 6: Using antifreeze without checking the manufacturer’s instructions
Never assume that automotive antifreeze or another household chemical is appropriate for drinking-water equipment.
Don’t introduce any chemical into an RO system unless it is specifically approved for that application and the manufacturer provides instructions for its use.
Mistake 7: Turning the system on without inspecting it
A fitting or housing could have cracked during storage.
Always inspect the system before restoring water pressure.
Mistake 8: Drinking the first water after long-term storage
After extended shutdown, follow the manufacturer’s flushing and startup procedure before using the water for drinking or cooking.
RO Winterization Checklist
Use this checklist before closing a property for the winter.
Before Shutdown
- Check RO filters
- Check membrane condition
- Inspect tubing
- Inspect filter housings
- Inspect storage tank
- Check for leaks
- Review manufacturer winterization instructions
Shutdown
- Turn off RO water supply
- Turn off storage tank
- Drain storage tank
- Open RO faucet
- Relieve system pressure
- Drain accessible water
- Follow membrane storage instructions
- Protect filters and housings
- Disconnect electrical components if required
Before Leaving
- Inspect for leaks
- Confirm water supply is shut off
- Confirm system is protected from freezing
- Document which components were removed
- Record filter and membrane dates
Spring Startup
- Inspect all components
- Reinstall removed components
- Turn water on slowly
- Check for leaks
- Flush system
- Replace filters if necessary
- Sanitize if appropriate
- Allow system to refill
- Follow manufacturer’s startup procedure
Winterizing an RO System FAQ
Can an RO system freeze?
Yes. Water remaining inside RO filter housings, tubing, tanks, membranes and other components can freeze if the system is exposed to freezing temperatures.
Do I need to winterize my RO system every winter?
Not if the RO system is installed inside a reliably heated home where temperatures remain above freezing. Winterization becomes important when the system may be exposed to freezing conditions.
Can freezing damage an RO membrane?
Yes. EPA guidance states that RO membranes that are not in use should not be allowed to freeze or dry out. Follow the membrane manufacturer’s storage procedure for extended shutdowns.
Should I drain my RO storage tank before winter?
If the system will be exposed to freezing temperatures, follow the manufacturer’s winterization procedure, which will typically address the storage tank and other water-filled components.
Can I leave my RO system running while I’m away for the winter?
If the property remains heated and the RO system is protected from freezing, it may be possible to leave it in normal operation. For an unoccupied property, however, shutting off the water supply may reduce the risk of an undetected leak. Follow the manufacturer’s recommendations and consider the overall plumbing system in the property.
Can I use antifreeze to winterize an RO system?
Do not use ordinary automotive antifreeze in a drinking-water RO system. Only use a product specifically approved for the application and only according to manufacturer instructions.
What happens if my RO system freezes?
Do not immediately pressurize a frozen system. Allow it to thaw naturally and inspect the system carefully for cracked housings, tubing, fittings, tanks and other damage before restoring water pressure.
Should I replace my RO membrane after winter?
Not automatically. If the membrane was properly stored according to the manufacturer’s instructions, replacement may not be necessary. If it froze, dried out when it should have remained wet, exceeded its service life, or shows reduced performance after startup, replacement may be appropriate.
How long can an RO system sit unused?
There isn’t one universal time limit. Storage requirements depend on the system, membrane and manufacturer’s instructions. For extended periods of non-use, follow the manufacturer’s shutdown and membrane-preservation procedure.
Final Thoughts
Winterizing an RO system is primarily about preventing freezing and properly preparing the system for an extended shutdown.
If your RO system is inside a heated home, normal maintenance may be all that’s necessary. But if the system is located in an unheated area or the property will be vacant with the heat turned off, taking the time to shut down and drain the system can help prevent expensive freeze-related damage.
The most important steps are to shut off the water, drain the storage tank, relieve system pressure, protect water-filled components from freezing, and follow the manufacturer’s membrane-storage instructions.
Don’t overlook the RO membrane. EPA guidance specifically cautions against allowing unused membranes to freeze or dry out, making proper membrane storage one of the most important parts of an extended shutdown.
When you’re ready to put the system back into service, inspect it carefully, restore water pressure slowly, check for leaks and thoroughly flush the system according to the manufacturer’s instructions.
For year-round maintenance—including filter replacement, membrane care, sanitization, tank maintenance and troubleshooting—see the Reverse Osmosis Maintenance Guide on Revosmo.com.
