(New) RO Membrane Not Working? Here Is What to Do!
Written by: Alexandra Uta // Last Updated: Mar 23, 2023
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While a reverse osmosis membrane should last a couple of years if it is treated right, there may be incidences where it doesn’t seem to be functioning as it should.
Having off-smelling or tasting water or having little or no water from your RO faucet could be signs that something is wrong with your membrane.
So, let us look at why your (new) RO membrane might not be working properly and what you need to do to fix it.
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Key Takeaways
There are several common explanations for why your (new) RO membrane may not be working:
- Feed water pressure is too low – increase.
- Feed water temperature is way too low – increase.
- Feed water TDS is too high – pre-treat.
- You need to flush your brand new RO membrane.
- There is a malfunctioning O-ring in the membrane housing – fix.
- RO membrane itself is misplaced – fix.
- You are using the wrong flow restrictor – replace.
- Fresh pre-filters are releasing carbon dust – flush.
- The RO membrane has reached the end of its life – replace.
- Pre or post-filters are clogged – replace.
- The check valve is blocked – clean or replace.
New RO Membrane Not Working?
If your RO membrane is new and has been properly installed, your pre-filtration systems are all working, and your scheduled maintenance has been performed, then an RO membrane not functioning is a very unlikely occurrence. However, it may happen, and this is what you need to look out for.
No or Very Little RO Water
Is your RO system not producing enough water? This may be a sign that the membrane is not filtering water, and some of those reasons may not be actually due to the membrane itself.
Feed Water Pressure Too Low
If your feed water pressure is too low, there won’t be enough ‘oomph’ to push the water through the RO membrane to begin with, resulting in not much filtered water, and a lot of wastewater.
If the issue is low feed water pressure, you will need to increase it, for example by installing a pressure pump. 40 psi is the absolute minimum, but 60 psi is even better.
Feed Water Temperature Too Low
Is your flow rate decreasing specifically in winter or when the temperature is cooler? An often overlooked factor for reduced output of filtered water is the temperature of the water itself. Cold water is ‘thicker’ and isn’t as good at pushing through the RO membrane.
This issue doesn’t mean you need a new membrane, but you might need to have some extra feed water tubing coiled up to allow time for the water to pass through it and raise it to room temperature. Alternatively, have the water lines near something warm. You can have the water at up to 95 degrees before it becomes too warm for the RO membrane.
Excessive TDS
Testing your feed water to determine its level of TDS (total dissolved solids) is also important. Feed water that is too high in TDS means your RO membrane is more likely to get clogged with these particles quickly, reducing the ability of the water to filter through.
Depending on the TDS level, you may need to install pre-treatment, such as a water softener, to combat this and increase the lifespan of your membrane.
Feed Water pH
The pH of your feed water can also cause issues with your RO membrane. If your water pH is off by a lot, it may affect filtration performance. RO membranes work best with water at a pH of around 7-8.5.But even as low as 5-6 should be fine.
Note: This is very rare!
High TDS in Purified Water
If you are finding a high level of TDS in your filtered water, this is a clear sign that your RO membrane is letting contaminants through.
Membrane Flushing Required
If your membrane is brand new, it can take a little while to properly hydrate, which makes the initial bit of water after a membrane change high in TDS. This level should drop after an hour or so, so it is important to flush the system and dispose of the first tank of water produced.
Misplaced, Missing, or Damaged O-Ring
During installation, the O-rings may have been damaged or not correctly inserted. Carefully unscrew the membrane housing and check that all the O-rings are in place.
RO Membrane Not Properly Seated
When putting the new reverse osmosis membrane itself in, it may not have been adequately inserted. Open the membrane housing to check that the membrane has been properly installed and is correctly seated.
Not the Right Flow Restrictor
A broken or blocked flow restrictor may be the issue. If you have had your flow restrictor for some time, especially if it has been used with hard water, it may be blocked. Changing the flow restrictor when you change your membrane is a good idea.
New Pre-Filters
If you have installed new carbon pre-filters at the same time as your new membrane and haven’t flushed the system, the carbon dust from the filter may be messing with your TDS reading.
What to Do When a Used RO Membrane Has Stopped Working
If you find there is an increase in the TDS of your output water, or if your reverse osmosis system seems to have stopped or significantly reduced its water output, here is what you need to do.
A Clogged RO Membrane – Check Performance!
Has it been a while since you changed your RO membrane? It may have just reached the end of its life. You can measure this by measuring the TDS level of the feed water versus the filtered water’s TDS level with a TDS meter. Use the following formula:
Rejection rate in % = (TDS of raw water – TDS of purified RO water) / TDS of raw water x 100.
If your rejection rate is below 80%, then time to replace the membrane!
How to Change a Bad RO Membrane
- Check the product manual; each system may have differences and slightly different membrane replacement procedures.
- Wash your hands, so you don’t foul the new RO membrane with oil from your fingers!
- Turn off the feed water and shut the storage tank valve.
- Open the RO faucet and let it run to depressurize the system. Turn it off when the dripping slows or stops.
- Remove the water line from the RO membrane housing cap.
- Turn the cap clockwise, and use a filter wrench if needed.
- Remove the old membrane, and use needle nose pliers if needed.
- Clean the inside of the membrane housing with warm dishwater and rinse thoroughly.
- Install the new membrane O-ring side first, ensuring it is all the way in and seated tightly.
- Check the O-rings on the housing cap before screwing it back on and reconnecting the tubing.
- Turn the water supply back on and open the RO tank valve.
- Open the faucet and let the system flush for several minutes while checking for leaks.
- Let the tank fill, and discard at least one full tank before use to fish out any preservative from the new RO membrane.
Further Reading:
Clogged Pre or Post-Filters
If your membrane doesn’t appear to be the issue, it might be your pre-filters. Having clogged pre-filters means they won’t be removing what needs to be removed from the feed water before it reaches the RO membrane, which could slow down its ability to filter water, lowering the output flow.
A Blocked Check Valve
A blocked check valve could also be an issue that lowers the flow of filtered water. A check valve that is not functioning properly can cause a backflow of water to the RO membrane, reducing its output ability.
If you have any questions about your new RO membrane not working please don’t hesitate to leave a comment below!
About the Author Alexandra Uta
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