How Often and When to Replace a Reverse Osmosis Membrane

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Reverse osmosis membranes can last for years on end, but their performance can be maximized with regular system maintenance and timely pre-filter replacements.

Knowing when and how often to replace your RO membrane is key to ensuring a quality supply of clean drinking water in your home.

In this article, we will look at some of the important factors to consider when deciding when to replace your reverse osmosis membrane, including your water conditions and usage.

Key Takeaways

  • RO membranes should generally be replaced every 2 to 5 years, but the timing depends on numerous factors, including the condition of your feed water and how strictly you adhere to pre-filter replacement schedules.
  • If you notice decreased water output, bad smells or taste in the water, a low salt rejection rate, or if your drainage seems to be running continuously, they may be signs your RO membrane needs to be replaced.

Schedule: How Often to Replace an RO Membrane

So, how often should you change your RO membrane?

Generally speaking, it is recommended that you replace your reverse osmosis membrane every 2-5 years. However, this can depend on a variety of factors, such as the amount of water used through the system as well as any potential contaminant levels present in the source water.

High levels of chlorine, for example, can cause earlier degradation of the membrane, as can high levels of iron and hard water. If you are regularly maintaining your system pre-filters, this will also increase the longevity of your RO membrane.

blue reverse osmosis membrane

Factors That Influence How Long Your Membrane Lasts

Water Usage

If you are using more water than what the system was designed for, this can quickly break down an RO membrane. If, on the other hand, your water usage is way below average, your reverse osmosis membrane may last longer than specified by the manufacturer.

Water Hardness Levels

Hard water contains higher concentrations of dissolved minerals, such as calcium and magnesium, which can significantly reduce the lifespan of an RO membrane over time due to fouling. Additionally, hard water can also clog parts of RO systems, causing them to fail prematurely.

It’s important to test your water hardness levels in order to get an accurate picture of how it may be affecting your RO system’s performance. Get a water softener if need be!


TFC membranes are sensitive to chlorine. Exposure can lead to decreased performance and, eventually, membrane replacement.

When chlorine levels surpass 4 parts per million, it can reduce the lifespan of your RO membrane. This is because chlorine causes the membrane to oxidize, which can break down its materials over time.

Other Impurities

Impurities such as suspended solids, heavy metals, organic compounds, and bio-contaminants can cause fouling on the RO membrane over time. These impurities may accumulate and create a buildup of deposits on the surface of the membrane. This buildup can interfere with the regular operation of the membrane, resulting in decreased efficiency and productivity and premature degradation or even failure of the membrane.

Membrane Age

As the membrane ages, it can become more prone to fouling, which reduces its permeability and efficiency. In some cases, the membrane may become saturated and require replacement.

As well, chemical cleaning may be required more often as the membrane ages because of accumulated organic matter.

Additionally, older membranes are less able to handle changes in water temperature or pressure than newer membranes. This could potentially lead to leaks or even failure of the RO system if not addressed promptly.

Overall System Maintenance

Taking good care of your reverse osmosis system as a whole is the key to membrane longevity. Most importantly, you need to adhere to the pre-filter replacement schedule. Only when sediment and carbon pre-filters are replaced on time can they remove dirt and chlorine from the feed water before it reaches the membrane stage.

Also, if an RO system is not adequately cleaned or sanitized from time to time, fungi and bacteria can colonize on the membrane surface and clog the pores.

How to Know When to Replace Your RO Membrane

It’s also important to keep track of how long you’ve been using your RO membrane. Depending on the amount of water you filter, an average RO membrane should last two to five years before needing replacement.

In addition, if you’re having frequent maintenance problems or noticing a decrease in filtered water quality with each filter cycle, then you should also consider replacing your RO membrane.

Finally, if you notice that your filters are clogging up or not doing their job as efficiently as before, this could be a warning sign that your membrane has reached its lifespan and needs to be replaced. Keeping track of filter changes, noting any changes in water taste or smell, and tracking TDS readings are all ways to help determine when it’s time for a new RO membrane.

Signs Indicating Your RO Membrane Is Bad

Bad Water Taste & Odor

RO water is odorless and tasteless. If your RO water develops any kind of taste or odor, it is a sign that your reverse osmosis membrane is not filtering the contaminants that cause them and will need to be replaced.

Slow Water Flow

A slow water flow may indicate that your RO membrane is clogged and not allowing enough purified water through. You will need to replace the membrane and the pre-filters and clean and sanitize the whole system.

RO System Doesn’t Stop Draining

A clogged or blocked membrane can cause an imbalance in the system’s water pressure. This pressure imbalance forces the water to drain instead of diffusing through the membrane and being stored in the tank as usual.

Product Manual

The product manual for your RO system will indicate the frequency at which your RO membrane should be changed. These guidelines should be followed, even if your RO membrane seems okay.

Low Salt Rejection Rate

This can be determined by measuring the total dissolved solids (TDS) in both the input and output water supply. If salt rejection is less than m 80%, then it is time to replace your RO membrane, as it is not properly removing your TDS anymore.

Measuring Membrane Performance Using a TDS Meter

To measure the salt rejection rate of your RO system, you will need to use a TDS meter. This is the most reliable indicator of when your membrane needs replacing.

tds meter in glass of water

  1. Test the TDS of the untreated water.
  2. Test the purified RO water.
  3. Calculate the TDS rejection rate with this formula: Rejection rate % = (TDS of untreated water – TDS of purified RO water) / TDS of untreated water x 100
  4. If the rejection rate is below 80 percent, it is time to replace the membrane.

Instructions for How to Change a Reverse Osmosis Membrane

  1. Check the product manual for specific instructions, as the process may vary slightly between units.
  2. Wash your hands, so you don’t contaminate your new filter element.
  3. Turn off the water supply and close the storage tank valve.
  4. Turn on the RO faucet to drain any remaining water. When the dripping stops, close the faucet.
  5. Place a bowl underneath the system.
  6. Locate the membrane housing on the RO unit and open it (you might need to remove some tubing).
  7. Carefully remove the RO membrane from its housing and dispose of it properly.
  8. Insert the right end of the new membrane into the empty housing and push down gently until you feel resistance.
  9. Reattach the housing cap and any tubing previously removed.
  10. Turn on the water supply, making sure there are no leaks.
  11. Flush the water for a few minutes to clear any remaining contaminants.
  12. Close the faucet and let the tank fill.

Why Is It Important to Replace an RO Membrane?

The longer an RO membrane remains in use without being replaced, the less effective it will be at removing water contaminants. Replacing an RO membrane regularly is essential for maximum performance and optimal filtration of your drinking water supply.

This will not only guarantee clean and safe drinking water but also help increase the lifespan of all components within the entire reverse osmosis system.

How Does an RO Membrane Work?

A reverse osmosis membrane works by allowing water molecules through it, but almost nothing else. The semipermeable membrane acts as a physical barrier. This allows particulate matter, salts, and other ions to be filtered out.

A pore size of 0.0001 microns means RO removes almost everything from a water supply. As such, RO purified water is ideal for drinking.

If you have any questions about how often to replace an RO membrane please don’t hesitate to leave a comment below!

About the Author Gene Fitzgerald

Gene Fitzgerald is one of the founders of BOS and currently head of content creation. She has 8+ years of experience as a water treatment specialist under her belt making her our senior scientist. Outside of BOS, Gene loves reading books on philosophy & social issues, making music, and hiking.
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