Best RO Membrane Filters & Replacement Cartridges

RO membrane and filter cartridges are perhaps the most important parts of any reverse osmosis system. They determine the overall performance of the RO process when it comes to filtering water and in this article, we will primarily focus on RO membrane and filter cartridges plus steps to replacing them.

Here is our list of the top 10 universal RO membranes that we believe are worth spending your hard-earned cash on should you need to change your old RO membrane.

The 10 Best RO Membranes in this review:

RO MembranesBrand
iSpring MC1iSpring
Film Tec TW30181275Film Tec
GE FX12MGE
Express Water FLTMEME50Express Water
FS-TFC FS-1812-50FS-TFC
APEC MEM-ES-50Apec Water
Water Filter Tree WFT-M50WFT
AP RainSoftRainSoft
APPLIED MEMBRANES 75 GPDAM
WFE TFC-RS9-12WFE

RO Membrane Filters

A reverse osmosis membrane (RO membrane filter) is a Thin-film Composite membrane (TFC) which is made up of three layers of semi-permeable materials that work as a molecular sieve that allows water molecules to pass through while stopping a wide variety of impurities and contaminants.

The three layers include a thin polyamide layer which is deposited on top of a polysulfone porous layer followed by a non-woven fabric support sheet below it.

This three-layer configuration is what gives the RO membrane a high rejection and filtration rate against undesired materials as well as good mechanical strength.

The pores of the membrane are sized from about 0.001 to 0.0001 micron which basically excludes most of the dissolved contaminants in the water as it passes through the membrane.

Aside from the Thin-film Composite (TFC) membrane, another common type of RO membrane used in household RO systems is the Cellulose Triacetate (CTA) membrane. What sets these two types apart is their filtration ability and chlorine tolerance.

CTA membranes are chlorine tolerant but tend to be more susceptible to organic fouling plus they have a rejection rate of only 93% against standard contaminants. TFC membranes, on the other hand, have an average rejection rate of 98% and are much less susceptible to organic fouling.

However, they may require carbon pre-treatment filters when dealing with chlorinated municipal water as they are mostly quite effective at purifying chlorine-free water.

Universal RO Membrane

Universal RO membranes are standard TFC RO membranes found in the most common household RO systems. For this kind of membrane, they can last for about 2 to 3 years.

Therefore, you will have to replace them after every 3 years, but they can go up to 5 years if you are dealing with softened water and take good care of your filter cartridges by replacing them on time.

You will probably need a TDS meter to help you check the TDS level in the purified water produced. This is the best way to determine when you should replace the RO membrane.

Branded RO Membrane

When it comes to replacing branded RO membranes, you will need first to figure out the brand and model of your RO system. You have to determine the brand and model number so that you can get the right replacement membrane or filter cartridges.

You can find this information on the plastic or metal manifold which holds the filters in place or on a small sticker on the back part of the manifold. However, the labels on the unit may not indicate the brand or model of the RO system.

The good thing though is that most brands of RO systems usually provide great customer support and even send the customers reminders of when it’s time to replace the membrane or filters on your system.

They may not also come with clear instructions on how to replace the RO membrane or filters but we are going to help you know how to do that now.

GPD Of An RO Membrane Filter

The GPD (gallons per day) of an RO membrane will determine the amount of water you can get on average. It’s the actual production rate of the RO membrane in terms of how many gallons of purified water it can produce in a day.

For under-the-sink and countertop RO systems, the common production rate you will find is 50, 75, 90, and 100 GPD.

There are also other RO membranes with much more capacity which are meant for large RO systems for the whole hose. These can have a GPD of 200, 300, or 500.

A 50 GPD-rated membrane is ideal for a common household of around 2 to 4 people while 75 90 and 100 GPD RO membranes are best suited for families of 5 to 8 people.

A 300 GPD or 500 GP RO membrane will be adequate if you are using the RO water for purposes other than for drinking like daily laundry, mopping the floor, and washing your utensils.

Keep in mind that the GPD performance of any RO membrane can go up or down depending on such factors as water pressure, water temperature, the total amount of dissolved solids in the water being filtered, condition of pre-filters, etc.

If your RO system uses a standard-sized membrane, then you can change it to increase the GPD in order to increase the daily production capacity of your RO system plus the speed at which the purified water is produced.

However, one thing you should note is that if you change your RO system membrane from the original size to a higher capacity, then you must change the flow restrictor as well because it is sized to go together with the RO membrane.

The size of the flow restrictor should properly match with the RO membrane capacity or rather the GPD. For instance, if you change from a 36 GPD membrane (uses a 350 ml per minute flow restrictor) to a 50 GPD membrane, then you will need a 500 ml per minute flow restrictor.

Flow restrictors help create pressure throughout the RO membrane as well as maintain a proper ratio of permeate (product) flow and reject flow (to the drain).

Therefore, the RO membrane GPD must match the flow restrictor to ensure that a proper balance is maintained between pure water and wastewater.

Not matching them properly could lead to excessive wastewater flow to the drain line or even cause premature membrane fouling.

How does An RO Membrane Work?

As I mentioned earlier, the RO membrane is made up of several layers of materials. On one side there is the polysulfone layer, on the other side is the impenetrable polyamide layer which is the actual purifying material and in the center is a perforated collecting tube. 

All these components of the membrane are then placed in one housing chamber which is designed to separate the filtered water from the waste or rejected water.

After the initial filtration through sediment filters and activated carbon filters, the feed water pressure forces the partially filtered water through the membrane chamber where it flows in a spiral direction starting from the top layer down to the center tube.

Inside the chamber, the polysulfone filtration layer allows the pure water to pass through leaving behind contaminants and other undesired particles.

The polyamide film is a nanofiltration membrane with high levels of dissolved solid rejection and water permeability. It possesses the properties that facilitate selective water permeation while restricting most other soluble contaminants.

From the polyamide layer, the purified water is channeled into a collecting tube in the center of the spiral wounds of membranes. The perforated collection tube then directs the purified water into a pressurized storage tank where it’s stored.

By pushing the feed water through the RO semi-permeable membranes, the natural osmosis process is reversed and overcame thereby leaving impurities behind down to 0.0001 microns while the filtered water molecules continue through the system.

The water is separated into two pathways. The wastewater containing the dissolved compounds and other organic and inorganic impurities is subsequently flushed down a separate drain line while clean, purified water goes into the RO tank for storage.

The polyamide layer is selected primarily due to its high permeability to water as well as relatively high impermeability to various kinds of dissolved substances like salts and other impurities including small, unfilterable molecules.

It’s responsible for the high rejection rate which is almost 98.99%. One innovative thing about the design of RO membranes is that it utilizes the same water pressure and flow to clean and rinse the membrane layers throughout the process.

The contaminants are flushed out and away on a separate line hence reducing waste build-up and accumulation inside the membrane chamber.

This feature protects the membrane from potential clogs and obstructions that are often caused by bio-fouling, contaminant saturation, and scale hardness.

Replacing RO Membrane

The RO membrane is actually the component that does all the work. The pre-filters prepare the water by removing most of the larger impurities that may cause damage to the RO membrane.

Typically, the lifetime of an RO membrane can be between three to seven years based on the water quality as well as application.

For softened water, you can get about 5 years out of your RO membrane provided you replace the other pre-filters regularly.  

For hard water or if you never flush the membrane, it may last a little shorter than 3 years. Even while the RO membrane is capable of rejecting most of the minerals, some of them can come out of solution and end up clogging several parts of its surface.

Therefore, you may need to replace the membrane in one or two years. A TDS meter can help you test your membrane and when the TDS starts to climb, then you will know that your RO membrane is beginning to go bad. To be on the safe side, we would recommend changing the membrane at least every three years.

Like I mentioned earlier, the RO membrane and filter cartridges are the most vital part of an RO system. The RO membrane is the component that actually does all the work.

The other filter cartridges like sediment and carbon filters are equally important as they prepare the water for the actual filtration by the RO membrane.  They protect the RO membrane from getting damaged to ensure optimal performance.

Therefore, you need to take good care of both the RO membrane and the filter cartridges and replace them at the right intervals.

Replacing the RO membrane will depend on the quality of your input water and the type of membrane you are using in your system.

Before starting, you need to turn off the water supply going into the RO system, close the ball valve on the storage tank and then turn on the RO faucet so that the water pressure can bleed out.

Once you’ve done that, follow the procedure below to replace your old RO membrane.

  1. Disconnect all the tubing from the RO membrane housing cap.  
  2. Unscrew the RO membrane end cap from the housing and slide out the old membrane. You may need a needle-nose plier to pull it out as it may be a little difficult.
  3. Rinse the inside of the membrane housing using warm water without soap (you can remove all the other cartridges and sanitize the entire system at this point if necessary)
  4.  Insert the new membrane inside the housing making sure that the O-ring sits securely and correctly otherwise your system won’t work. The O-ring end should go first.
  5. Screw the end cap back onto the membrane housing while also ensuring that the O-ring is still securely in place.
  6. Re-connect each tubing into their correct location making sure they are properly secured as well. You should re-install the tubing to correct fittings as far as possible.
  7. Now, open the water supply valve and turn on the RO faucet. Let it run until there’s a steady dripping. Check for leaks.
  8. Turn off the RO faucet and let water flow into the storage tank and check for leaks again. If there’s none, then your RO system is ready for use (don’t drink the initial water produced after the membrane replacement)

We also looked at several RO filter cartridges replacement sets on the market and picked some of the best options that are equally worth considering.

RO membrane & Replacement Filter Cartridges

Reverse Osmosis Replacement Filter Cartridges

RO filter cartridges are simple, modular filters which are made up of media that’s used to capture and remove particles that might otherwise block the small spaces between the RO membrane layers as well as the submicron particulates that may foul the membrane surface.

They consist of pre-filters and post-filters with the pre-filters comprising mostly a sediment filter which makes the first stage of the RO filtration process, a granular activated carbon filter that makes up the second stage, and an activated carbon filter which takes the third stage in the RO filtration process.

These pre-filters can range from 10 to 5 microns and capture most of the sediments, chlorine, fine particulates, and a number of other contaminants.

The post-filter, on the other hand, is mostly another 5-micron activated carbon filter that takes up the 5th stage in the RO filtration process and polishes the purified water from the RO storage tank as it’s channeled to the RO faucet.

The water produced by the RO system is highly pure but slightly acidic and as such some RO systems include a 6th stage in the RO filtration process which consist of a remineralization filter that introduces healthy minerals in the water, particularly calcium and magnesium, which as well help balance the pH level of the water and improve its test.

Some RO systems also have a 7th stage filter which is an UltraViolet filter that uses UV rays to destroy any biological contaminants such as harmful bacteria, viruses, fungi, E. coli, and microbes. 

Each of these filters is inserted into housing where the impurities are left behind in the filter material as the water flows through.

Replacing RO Filter

To ensure the optimal performance of the RO system particularly the RO membrane, it is crucial to maintain the filter cartridges and change them on time.

You should schedule the change on a regular basis because the contaminants from the water can clog the filters within a short time without frequent cleaning. This will affect both the quality of the water and the filtration capacity of the entire system.

Typically, the main RO filter cartridges which consist of the pre-filters should be changed every 6 to 12 months based on how bad the feed water is or how much water you purify. In other words, you should change your sediment and carbon filters at least once a year.

If you have an RO system that produces a large amount of pure water, then the cartridges are likely to get saturated by contaminants quickly. They can get exhausted within 3 months, hence you will need to change them more often.

If you continue to use the filters for a prolonged time without changing them on time, then chances of contaminants and other impurities passing into the water you drink are high which in turn can be harmful to your health.  

Like in the membrane replacement, you need to first shut off the main water supply going into the RO system before starting. Close the ball valve too and turn on the RO faucet to relieve the pressure in the unit. Let the stems stand for about a minute.

Put a shallow tray right under the filter housing to collect any water that can spill while changing the filters.  Now you can start the replacement as follows:

  1. Unscrew the filter housings by twisting and rotating them counterclockwise. Remove the caps and the old filters, for stubborn filter housing use a filter housing wrench.
  2. Make sure to carefully remove the O-rings too without tearing or damaging them. Put them on a clean surface.
  3. Rinse out the filter housings thoroughly with warm water and a bit of liquid soap but make sure all soap is completely rinsed out before placing the new filters.
  4. With a soft clean towel, wipe the O-rings clean and visually inspect them for cracks, tears and blemishes. A damaged O-ring may not seat properly inside the housing. So, if any of the O-rings appear damaged, then replace it.
  5. Lubricate each of the O-rings slightly using a silicone lubricant and insert them back into their respective housing. Make sure the O-rings are properly seated into their grooved area to provide the watertight seal between the caps and the filter housings.
  6. Now insert the new filter cartridges inside their respective housings and re-inspect the O-rings to ensure proper seating.
  7. Screw back the filter caps to the housing, hand tightening only. You should measure the new filters just to be certain they are of proper length and type.
  8. Turn the water supply valve on as well as the RO faucet and let it run while checking for integrity of the system to ensure there are no leaks.
  9. Let a few gallons of water run through the system and out through the RO faucet while the storage tank is still closed. You should get a steady stream of water which means the new filters are working correctly.
  10. Turn off the faucet and then open the RO storage tank ball valve and let the tank fill completely. Now your system is all set for use.

We also looked at several RO filter cartridges replacement sets on the market and picked some of the best options that are equally worth considering. Below are our reviews of the top 10 sets we picked.

10 best RO filters replacement sets in this review:

RO Replacement Filter SetsNumber Of Cartridges
iSpring F5-755 cartridges for 5 stages
Geekpure RO5-55 cartridges for 5 stages
Express Water FLTSETS6C6G6I3M50223 cartridges for 5 stages
General Electric FQROPF2 cartridges for 2 stages
iSpring F7-GAC7 cartridges for 4 stages
APEC FILTER-MAX-ES505 cartridges for 5 stages
APEC FILTER-SET3 cartridges for 3 stages
APEC FILTER-SET-ES3 cartridges for 3 stages
Whirlpool WHEERF2 cartridges for 2 stages
iSpring F28K7528 cartridges for 6 stages

Conclusion

The effectiveness and productivity of any RO system solely rely on the quality and efficiency of the RO membrane and filter cartridges it has.

Therefore, it’s vital to ensure that all these components are in perfect condition so that they can perform optimally and guarantee a constant supply of quality, clean purified water that’s safe and free from all harmful contaminants that may pose danger to your health and that of your family.

All the RO membranes and the replacement filter cartridge sets listed herein are of great quality and come at a very affordable price.

Most of them will fit any standard under-the-sink RO system as well as any standard 12-ich RO membrane housing and standard 10-inch filter housings.

If your current membrane or filter cartridges are not standard, then you will have to get a new housing along with the replacement RO membrane or filter set.