When winter temperatures arrive, professional window cleaners need to think about more than frozen hoses and icy conditions. One of the biggest concerns is protecting the reverse osmosis (RO) membrane inside their pure water purification system.
Whether you’re using a portable RO/DI cart, truck-mounted system, or stationary setup, a single freezing event can permanently damage an RO membrane, resulting in costly repairs, poor water quality, and unexpected downtime.
Here’s what you need to know to protect your investment.
How Freezing Temperatures Damage an RO Membrane.
RO membranes remove dissolved minerals and impurities from water, helping produce the purified water needed for spot-free window cleaning.
Even after shutting down your system, water remains inside the membrane’s housing. When temperatures reach 32°F (0°C) or below, that water can freeze and expand, potentially damaging the delicate membrane structure.
Freeze damage can cause:
- Reduced RO membrane performance and mineral rejection.
- Higher total dissolved solids (TDS) readings.
- Faster DI resin exhaustion and increased operating costs.
- Cracked membrane housings, fittings, or connections.
- Water leaks and reduced system efficiency.
Pro Tip: Don’t wait until temperatures reach freezing to protect your equipment. Consider taking precautions whenever overnight temperatures are forecast to drop below 40°F. Remember, an enclosed trailer or unheated garage won’t necessarily prevent freezing.
How Can You Tell If Your RO Membrane Has Freeze Damage?
Unfortunately, freeze damage isn’t always visible. Your system may continue producing water even when the membrane is no longer performing properly.
One of the easiest ways to identify a potential problem is by checking your RO membrane’s TDS rejection rate.
For example, if your incoming tap water measures 300 PPM and your RO output measures 15 PPM, your membrane is achieving a 95% rejection rate.
However, if your RO output suddenly increases significantly under similar operating conditions, the membrane may be damaged.
RO Rejection Rate Formula:
(Incoming TDS – O Output TDS) ÷ Incoming TDS x 100
Other warning signs include unusually fast DI resin consumption, visible leaks, cracked housings, or inconsistent water production.
Important: Always measure TDS immediately after the RO membrane and before the DI stage may still be removing the remaining minerals.
Can a Frozen RO Membrane Be Saved?
Not necessarily. If freezing has damaged the membrane internally, replacement is generally the most reliable solution.
However, exposure to freezing temperatures doesn’t automatically mean your membrane is ruined.
If you suspect your system has frozen:
- Move the equipment into a heated environment and allow it to thaw naturally.
- Inspect membrane housings, fittings, and connections for damage.
- Once completely thawed, restart the system according to the manufacturer’s instructions and check for leaks.
- Test your incoming and RO output TDS to evaluate membrane performance.
Never operate a system while its components may still be frozen ,and avoid using excessive heat to accelerate thawing.
How to Protect Your RO/DI System During Winter
Preventing freeze damage is considerably less expensive than replacing damaged equipment.
Here are a few important precautions:
- Store equipment in a heated location. A temperature-controlled garage, warehouse, basement, or workshop is ideal.
- Don’t rely on draining alone. RO membranes can retain water internally even after hoses and housings appear empty.
- Follow proper winterization procedures. Consult your equipment manufacturer’s recommendations for extended storage. Never use automotive antifreeze or unapproved chemicals. Automotive antifreeze typically contains ethylene glycol or propylene glycol, along with corrosion inhibitors, dyes, and other additives. These substances can contaminate the RO membrane and downstream DI resin. Both AXEON Water and Parker specifically warn against using ethylene-glycol automotive antifreeze in RO systems.
- Protect the entire system. Pumps, filter housings, DI vessels, hoses, and fittings can also suffer freeze damage.
- Monitor storage temperatures. A temperature with a low-temperature alert can provide additional protection.
Pro Tip: Before starting your spring window cleaning season, check your RO membrane’s rejection rate and inspect the entire purification system for leaks or damage.
Why Freeze Protection Matters
A damaged RO membrane can create expenses beyond the cost of replacing the membrane itself.
When an RO membrane losses efficiency, more dissolved minerals pass through to the DI stage. This causes your DI resin to become exhausted faster, increasing operating costs.
Additional repairs, equipment downtime, and inconsistent water quality can make the problem even more expensive.
For professional window cleaners who depend on their pure water systems daily, proper winter storage is a simple way to avoid unnecessary expenses.
Final Thoughts: Protect Your Investment This Winter
The bottom line is simple: Never allow your RO membrane or other water-filled purification components to freeze.
Whether you’re storing your equipment overnight or shutting down for the winter season, proper storage and manufacturer-approved winterization procedures are essential.
Taking a few preventative steps now can save you from expensive repairs and unexpected downtime when business picks back up.
Need Help With Your Pure Water System?
At Detroit Sponge & Chamois Co., we’ve been helping professional window cleaners find the right equipment and supplies for over 85 years.
Whether you need a replacement RO membrane, DI Resin, purification accessories, or help troubleshooting your system, our knowledgeable and friendly team is happy to assist.
Visit www.detroitsponge.com
Phone: 1-800-535-6394
Email:customerservice@detroitsponge.com
Detroit Sponge & Chamois — Proudly serving professional window cleaners since 1938.