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5 Ways to Tell if RO Membrane is Bad

Scott Winfield
Written by Scott Winfield
Last Updated on

Reverse osmosis (RO) membrane is a thin film consisting of several different materials. It’s mostly made of polypropylene or another synthetic polymer.

These semipermeable films effectively remove chemicals and other contaminants from water thanks to their very small pore size, which is 0.0001. As a result, larger particles like minerals, organics, and bacteria can’t pass through.

The average lifespan of an RO membrane is one to two years and they don’t require regular maintenance. However, it’s not uncommon for them to wear out and stop working as they should.

If you suspect that’s the case with yours, we’re here to help you out. Below are tell-tale signs that your RO membrane needs replacing:

1. Discoloration Is a Sign of Bad Membrane

As the membrane filters incoming water, impurities in the water are left behind and coat its contact surface. If these impurities aren’t removed or regularly washed away during the RO process, they can build up and change the color of the membrane.

 RO Membrane Discoloration
RO Membrane Discoloration

One quick way to tell if your membrane is discolored is to look at your water filtration system. The membrane is a part of the system that is left exposed to air; you should be able to tell if it’s stained or discolored.

If it’s discolored, it should immediately be replaced to prevent further damage.

2. Reduced Flow Rate Might Be a Sign Of Faulty Membrane

A reduced flow rate could mean that your membrane is either clogged or is allowing too much water to pass through it. If the membrane is clogged, it will be unable to block larger contaminants, resulting in low water flow.

Reduced Flow Rate

If the membrane allows too much water to pass through, it could be due to either a buildup of impurities or a breakdown of the membrane itself.

A clogged or faulty membrane can be corrected by throughly cleaning it. If the membrane is still clogged after cleaning, then you should consider completely replacing it.

3. Foul Smell May Indicate Bad Membrane

The RO membrane can become fouled over time by dirt, sediment, and other contaminants.

When this happens, the membrane becomes less effective at removing impurities, and water produced by the system can have bad taste or odor.

RO Membrane Foul Smell

Unfortunately cleaning the membrane may not be enough to remove the foul odor. You should consider completely replacing it.

4. Lukewarm Water

If the filtration system is working as it should, the water that’s being pushed through should be lukewarm. If it suddenly gets hotter than lukewarm, it could indicate too much pressure is being applied to the system.

Tepid RO Water

When there’s too much pressure, the membrane can start tearing. It would cause water to be pushed back too quickly, resulting in a rise in temperature.

Once again, the only solution is to replace the membrane. Otherwise, the water quality will only get worse.

5. Cloudiness In The Membrane

If you notice your RO membrane is beginning to develop a cloudy look, it could mean that the membrane is being contaminated with minerals. If minerals are being pulled from the feed water, they can build up on the membrane, reducing performance.

RO Membrane Cloudiness

If the membrane contamination is due to minerals, it’s best to clean or replace it before it damages the rest of the system.

How Long Does an RO Membrane Last?

An RO membrane can last for 2-5 years with proper care and maintenance. However, if left unchecked, the membrane can suffer from several problems that can shorten its lifespan.

To ensure your membrane lasts as long as possible, it is essential to have it regularly cleaned or replaced if wear and tear.

Additionally, the type of water being filtered can also impact the lifespan of an RO membrane. For example, water with a high mineral content can be more corrosive and cause more wear and tear.

What Causes Damage to Membrane?

Several factors can cause damage to the membrane. The most common cause is an increase in differential pressure, which can happen when the system isn’t working correctly or when there is a blockage.

Another common cause of damage to the membrane is the back pressure phenomenon, which happens when water pressure in the system is too high and causes the membrane to rupture.

Abrasion processes from fouling can also cause damage to the membrane, which happens when deposits build up on the surface of the membrane and cause it to wear.

Massive or micro-damage from scaling can also cause damage to the membrane, which happens when deposits build up on the surface of the membrane and cause it to crack.

Oxidation processes or even degradation with time can also cause damage to the membrane.

How Much Does RO Membrane Replacement Cost?

The cost of replacement membranes can vary widely, from as little as $60 to more than $200 per year. The average price is typically between $80 and $90. The more filters your system has, the more expensive it will be to replace them.

Depending on the brand and model of your system, you should replace the RO membrane every 6 to 12 months.


There are a couple of ways to identify a bad RO membrane such as dis-coloration, sudden decrease in the flow rate, foul taste or smell, lukewarm water, and cloudiness in the membrane.

There’s nothing much you can do about a bad membrane, either. There’s only one solution to all of these problems: replacing it.

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Scott Winfield
Scott Winfield
My name is Scott Winfield and researching and writing about water filters and other strategies to purify water has become my full time passion in recent years. I'm glad that you found our site and you can look forward to authoritative and well researched content here to help you get the best in water.
  1. Very informative and comprehensive article. Answered a lot of my questions. I do have a couple tho. I have a K5 Kinetico system, Would adding a mineral filter bring the acidic
    RO up to alkaline? Talked to Kinetico but they don’t know by how much. Adding baking soda to alkalize water. Thanks, and have a great day.

    1. Hi Jim, thank you for reading and glad you found the content useful. The mineral filter should be a good solution to add back in calcium and magnesium for your drinking water. I would think that the ph should also come to a decent level. If you have any doubts about this after you have the filter installed, it’s easy to use a ph strip to test your water for the acidity/ph level with one of these kits.

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