Do you know how to tell when your Reverse Osmosis membrane needs to be replaced?
It can be difficult to tell if your RO filter is still working properly or if the membrane needs to be replaced. There are several factors that affect the life of an RO membrane and it performance. Knowing how your RO system works will help you determine when the membrane should be changed.
In this article, I will go over some of the warning signs that your RO membrane may need to be replaced so that you can be certain your water treatment system is working properly.
How Does a Reverse Osmosis Filter Work
The membrane filter is the key element of your reverse osmosis system. It removes dissolved solids and other contaminants by filtering out large molecules like lead, PFAS, and heavy metals while allowing water to pass through.
The RO membrane is a thin sheet of plastic with tiny holes. These small pores allow water to pass through while blocking out larger molecules, ions and contaminants.
As the filter becomes more used over time it will start to clog up with waste material from your tap water that can reduce its effectiveness as a membrane filtration device. When this happens, your RO system will not work as well as it should, and you may start to see a decline in water quality.
Most residential RO systems include filters to enhance the performance of the membrane. Additional filters you may find on a reverse osmosis system include:
- Sediment filter: a sediment filter removes turbidity, suspended solids, and other particles to protect the RO membrane from fouling.
- Activated carbon filter: activated carbon is used to remove chlorine that can oxidize and damage the RO membrane as well as volatile organic compounds that can degrade the membrane.
- Post-filter: many RO systems include a second filter that includes activated carbon as a polishing step.
These ancillary components are important to the proper functioning of your RO system and must be properly maintained. Following the guidelines in this article will maximize your membrane life.
I recently installed a reverse osmosis filter under my kitchen sink. It is easy to maintain and doesn’t take up a lot of space. You might want one for your home.
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When to Replace RO Membrane
If you are unsure whether your RO membrane needs to be replaced, there are several warning signs that you can look for. These include:
- A decrease in water flow
- Poor water quality or taste
- High levels of dissolved solids or contaminants in the water
- Continuous draining of water
- Leaks from fittings or filter cartridges
- Unusual noises
- Manufacturer’s recommendation
Read my comprehensive guide on how to evaluate your RO system’s performance.
1 – A decrease in water flow
One of the most common signs that your RO membrane needs to be replaced is when you notice a loss in water flow. As the filter membrane becomes fouled, your water supply will experience a pressure drop, resulting in a drop off in flow. If you notice a significant decrease in water flow, it is likely time to replace the membrane.
2 – Poor water quality or taste
Another common warning sign that your RO membrane needs to be replaced is a change in the overall quality of the water. You may notice a decrease in its clarity, changes in color, the presence of an odor, or an unusual taste. These changes are caused by particles or scale clogging up the pores on your RO membrane. When this happens, it is time to replace the membrane.
3 – High levels of dissolved solids or contaminants in the water
You should routinely measure the total dissolved solids (TDS) of your treated water. An increasing level of TDS indicates that your RO membrane is no longer removing all of the dissolved solids and other contaminants from your water. This can be an indication that it is time to replace the membrane.
If you are seeing a continuous rise in the TDS levels or if your water tastes bad, then it is definitely time to replace your membrane filter.
4 – Continuous draining of water
If you notice that the waste water is continuously being drained, this could be a sign that there are leaks in the system or the RO membrane has failed and needs to be replaced. Look for signs of wetness around fittings on hoses, at connections points where hoses are attached or around any fittings on the RO membrane housing. If you notice excessive moisture in these locations, then it is likely that there are leaks and your filter may need to be replaced.
5 – Leaks from fittings or filter cartridges
If you start noticing large amounts of water draining out of a fitting while the system is running this could mean that the RO membrane is leaking. You can check for leaks by inspecting the filter cartridge and fittings for any moisture or water droplets. If you find evidence of a leak, it is likely time to replace the membrane.
6 – Unusual noises
If you are hearing unusual noises coming from your RO system, it could be an indication that there is something wrong with the filter. This could include a loud hissing or gurgling sound; this is typically caused by air bubbles in the system and can be fixed with a simple adjustment to your RO system.
7 – Manufacturer’s recommendation
Your RO filter manufacturer provides a recommendation for when to change filters and perform other critical maintenance on your system. Always consult their guidelines to ensure that you are following the recommended replacement schedule for your specific RO system.
As a general rule, it is always best to replace all of the filters in your water treatment system at the same time – including the membrane filter. This will help ensure optimal performance and extend the life of your system. If you are unsure of when to replace your RO membrane, or have any other questions about maintaining your water treatment system, you should contact the manufacturer or consult with a water treatment professional.
You should also clean and sanitize your RO membrane routinely to keep it free of bacteria and improve its performance.
How Long Should a RO Membrane Last?
A reverse osmosis filter should last two or more years – if it is properly maintained. Follow the manufacturer’s guidelines for replacing membranes and other critical maintenance. Always consult with a water treatment professional if you have any questions about maintaining your RO system.
Read my comprehensive guide on reverse osmosis maintenance.
RO water filter life
The lifespan of an RO membrane depends on several factors, including the quality of the feed water, how much water it processes, the hardness of your water, chlorine levels, and how well you maintain it.
Most RO filter manufacturers recommend replacing membranes once every 12 to 24 months. Each system is unique, so you need to consult your owner’s manual for the changeout schedule for your unit.
As a general rule, it is best to replace all of the filters in your water treatment system at the same time. This will help ensure optimal performance and extend the life of your RO membrane filter.
The following table presents the recommended replacement schedule for your reverse osmosis membrane and the other system components. It also provides the average cost for replacement filters.
| RO System Component | Recommended Replacement Period | Average Cost |
| Particle filter | 6 – 12 months | $8 – $48 |
| Activated carbon filter | 6 – 12 months | $9 – $63 |
| RO membrane | 24 months | $25 – $280 |
| Post carbon filter | 12 months | $12 – $64 |
| Remineralizer | 3 – 6 months | $19 – $53 |
| UV lamp bulb | 12 months | $22 – $98 |
| Cleaning and sanitizing | 12 months | $15 |
Some of the RO system components need to be serviced or replaced every six to nine months. The major components should be checked and maintained between two and five years.
Factors that Effect Osmosis Membrane Life
The life of an RO membrane can be affected by several factors such as the type of water being filtered, the amount of contaminants present and the condition of the membrane filter itself. Generally, an RO membrane will last for approximately two to three years with proper care and regular cleaning.
1. Water hardness
Water that is very hard tends to form scale on plumbing components, including the RO membrane. These deposits can clog the pores of an RO membrane and reduce its efficiency.
Osmosis systems are not designed to work with excessively hard water. This is why it is important to use a water softener if you have hard water, before sending it to the RO system.
2. Chlorine levels
High levels of chlorine in your water can also damage an RO membrane over time. Chlorine is a powerful oxidizer that can degrade the polymer membrane. This is why it is important to use a carbon filter to remove chlorine from your water before sending it to the RO system.
3. Volume of water treated by your filter
The membrane in your RO filter has a finite life and can only treat a limited volume of water. If your RO system is treating large quantities of water, the membrane will need to be replaced more often than if it is only processing a small amount of water.
4. Time in service
RO membranes should last two or more years – if they are properly maintained. Follow the manufacturer’s guidelines for filter replacement and other critical maintenance. If the membrane has been in service for more than a year, it may be approaching the end of its usable life. Most RO filter manufacturers recommend changing them once every 12 to 24 months for optimum performance.
5. Quality of maintenance
The level of service and maintenance that your RO system receives, will affect the life of the membrane and other filters. If the filters are not cleaned or replaced when necessary, they will become clogged and less efficient. This can ultimately shorten the life of your RO membrane.
Ensure that you are following the recommended replacement schedule for your specific model to help maximize filter life and ensure optimal performance, while also protecting it from premature failure due to wear-and-tear.
You can often reverse the fouling that naturally occurs through consistent service and maintenance of your system.
How to Measure the Performance of Your RO System
The best way to know if your RO filter membrane needs to be replaced is to measure its performance.
Laboratory analysis or home test kits
The best approach is to sample the treated water for the contaminants you are treating – lead, PFAS, VOCs, mercury, metals. However, this can be expensive because you may have to submit water samples to a laboratory or purchase home test kits.
Total dissolved solids meter
Another effective way to measure your RO system’s performance is to measure total dissolved solids (TDS) with a TDS meter. A TDS meter measure the dissolved solids in a water sample, including minerals, salts and metals. This can be helpful in determining if the membrane is still removing contaminants from your water.
If the TDS level of the water being treated by your RO system increases over time, it may be an indication that the membrane needs to be replaced. You can also use a TDS meter to measure the TDS level of your untreated water and compare it to the TDS level of the treated water. This will help you determine if the RO membrane is still effectively removing contaminants from your water.
You can purchase a very accurate TDS meter for less than $25.
TDS water quality goals
The TDS of your treated water should be less than 100 parts per million (ppm). My under-sink RO filter consistently produces water with TDS values less than 10 ppm. This is a level that most RO systems can meet.
If your filter cannot reduce the TDS below 100 ppm, you should check with the manufacturer. It may be worth sending your water to a laboratory to test for the specific contaminant you’re worried about to be certain the filter is removing it.
RO Membrane Maintenance Schedule
I recommend following the manufacturer’s recommendation for filter and membrane replacement. They designed and built the unit, and they know what it takes to keep it functioning properly.
When to change the RO membrane
The typical RO membrane should last for 12 to 24 months. Some are designed to be in service for several years. Consult the manufacturer’s recommendations for when to replace RO membrane.
When to change the sediment filter
Sediment filters protect the RO membrane from solids, turbidity, and solids that can foul and plug the pores. They should be replaced every 6 months or as recommended by the manufacturer. If you’re treating a lot of water or if your water is not clear, you should replace the sediment filter more freqently.
When to change the activated carbon filter
Activated carbon filters protect the membrane from oxidation from the chlorine and other degradation from VOCs and other contaminants. They should be replaced every 6 months or as recommended by the manufacturer. High treatment volumes require more frequent carbon filter replacement.
When to change the post filter
The post filter removes any impurities that aren’t taken out by the RO membrane. Although this filter doesn’t affect the life of the membrane, it is important that you replace it routinely to ensure your water is clean and pure.
Final Take on RO Membrane Replacement
The RO Membrane is the heart of your water purification system. It removes all potentially harmful substances and contaminants from your drinking water, making it safe for human consumption. One question many people have is how long should a filter last?
The average membrane will last between one and five years depending on the quality of your water source, how well you maintain your system, the quantity of water you use, and other factors.