RO Filters: The Ultimate FAQ Guide

There are many brands and specifications of RO filters on the market, and choosing the best RO filter can be a daunting task.

This guide will make it easy for you by exploring all the information you need about reverse osmosis membrane filters.

Let’s dive right in.

Contents hide

1. What Is A RO Filter?

RO membrane can intercept substances with particle diameters between 0.001-0.0001 microns and is the product with the highest filtration accuracy in current membrane separation technology. RO is the abbreviation of Reverse Osmosis. Simply put, an RO membrane filter is a filter membrane with a reverse osmosis configuration. Its main function is to remove pollutants or debris from the water.

RO water filter is a semi-permeable layer that you push water through under pressure to deionize or demineralize it. The RO membrane used in the RO membrane filter is a thin layer of semi-permeable polymer adhered to a thick support layer. The most commonly used reverse osmosis membranes typically consist of thin-film composite membranes consisting of three layers: a polyester support mesh, a microporous polysulfone interlayer, and an ultra-thin polyamide barrier layer on the top surface.

Figure 5. Replacement filters for water treatment

2. How Do A RO Membrane Work?

The RO membrane is specifically the most vital element in any reverse osmosis system. The membrane typically comprises two semipermeable material sheets that are 2” –  8” inches in diameter. They are spiral wound and designed to keep back contaminants while letting clean water flow through. Forty inches is the standard length for RO membranes that are intended for use in industrial applications.

These membranes are put into housings, usually six at a time. These housings are then arranged for many parallel flow stages or streams. This means that reverse osmosis can occur in many stages. Osmosis is reversed using force and pressure from a pumping system.

The pumping forces feed water through the semipermeable RO membranes. This will forcefully reverse the natural process of osmosis and leave all contaminants behind. Meanwhile, the clean water will flow through the system.

Once this process is complete, you can use the highly purified water for other purposes. You can recycle, drain, or flush the filtered impurities.

Figure 3 RO membrane design.

3. What Materials Are RO Membrane Filters Made From?

The RO membrane filter is primarily a thin composite film membrane that consists of three layers.

These layers are:-

  • An ultra-thin polyamide layer- this acts as a barrier layer on the membrane’s top surface.
  • A microporous interlayer made from polysulfone.
  • A support web made from polyester.

These materials are best suited because they are customizable to sizes appropriate to efficient reverse osmosis processes, i.e., <200 nm for the polyamide layer.

They can also achieve pore sizes as tiny as 0.0001 microns.

ro membrane filter

4. What Are The Components Of RO Filtration System?

The components are:

  • An optional pressure regulator. This allows you to inspect and control the feed water pressure in your reverse osmosis system.
  • Sediment pre-filter. This component removes insoluble oxides and debris that may plug the drain flow restrictor or clog the membrane surface.
  • Carbon filter for chloramine and chlorine removal. Chlorine and chloramines degrade the RO membranes very easily. This filter protects the membrane from quick deterioration.
  • Shut off the valve. You can use this valve to cut off the water supply or to eliminate drain flow.
  • Reverse osmosis membrane. This is the most important part of the system. Its main purpose is to remove dissolved solids like metals or salts from the feed water.
  • Post filter to remove any remaining odors or tastes from the water.
  • Pressurized water storage tank.
  • Water supply.

5. What RO Filter Works Best For Each Application?

CTA membrane filters are more susceptible to fouling than TFC/TFM but are more tolerant to chlorine. They reject up to 93 percent of common impurities; use this type if your budget requirements cannot cater to auxiliary equipment like carbon filters.

TFM or TFC reject 98 percent of impurities and are not easily affected by organic fouling. The downside to this type is that you can only use it to purify water without chlorine content. If you wish to do so, you must use a carbon pretreatment filter.

6. In What Way Is The RO Filter Similar To Regular Distillers?

The water obtained through reverse osmosis and distillation is pure water. The working principle of ordinary distillers is condensation, while the working principle of RO membrane filters is membrane filtration. Both conventional distillers and reverse osmosis membrane filters can remove most substances from the water, reduce the level of contaminants in the water, and produce pure water.

Distilled water is mostly used for medical and industrial water because of its high purity and high production cost. The reverse osmosis method is widely used in laboratory, medical, commercial pure water, household pure water, and industrial water treatment fields due to its high filtration accuracy, relatively low cost, and less energy loss.

7. What Is The Difference Between Distilled Water And RO Filted Water?

RO water is water filtered through a reverse osmosis membrane and can also be called pure water. The reverse osmosis process can remove 98% of soluble salts and harmful substances in raw water. However, since the pore size of the reverse osmosis membrane is generally between 10A and 100A, it will also retain some ionic impurities.

Distilled water is water obtained by taking advantage of the difference in volatility of the components in a liquid mixture to vaporize H2O and then partially condense and separate the vapor. Distilled water is water that is ideally free of any impurities. But in fact, during the distillation process, volatile impurities such as carbon dioxide, ammonia, silica and some organic matter cannot be removed, and distilled water still retains some pollutants. In addition, fresh distilled water is sterile, but bacteria can easily multiply after storage.

8. What Is The Functional Lifespan Of An RO Filter?

Typically reverse osmosis membranes should last at least five years. Several factors can affect the lifespan of a reverse osmosis membrane filter, such as the nature of the water being treated. We recommend that while choosing high-quality reverse osmosis membrane filters, regularly replace worn parts and perform repairs/maintenance to extend the life of the equipment and reduce the cost of maintenance consumables.

Microfiltation Membrane3

9. What Contaminants Do RO Filters Remove?

The RO membrane removes dissolved contaminants and impurities like fluoride and arsenic through the membrane. They have a broad range of reductions due to their inclusion of sediment and carbon filtration. The carbon filter removes odors, bad taste, and chlorine, while the sediment filter rids debris and dirt.

The RO membrane filter removes the following chemicals:-

  • Pesticides and herbicides.
  • VOCs
  • Arsenic
  • Chlorine
  • Sediments
  • Salt
  • Fluoride

You should note that the RO membrane filters do not remove viruses and bacteria. It may initially remove bacterial contaminants, but the contaminants may grow on the RO membrane. This may contaminate your water supply and potentially put your health at risk. We recommend UV Disinfection if you want to remove viruses and living organisms from your feed water.

10. Do RO Water Filters Remove Important Minerals?

Yes. The RO membrane has the characteristics of high filtration accuracy, so the RO membrane filter can remove nearly 97% of the total mineral content in the water, remove the hardness in the water, and obtain delicious drinking water while reducing the formation of scale.

The use of RO pure water machines in the home can remove soluble salts and optimized substances including calcium and magnesium ions, making the water produced healthy and safe. If you are worried about the impact that mineral deficiency may have on your health, you can also choose a home water filter that retains minerals or obtain the minerals you need daily through food.

11. Do RO Filters Require Electricity To Work?

RO membrane filters only require water pressure to work. But in a membrane filtration system, you typically need an inlet pump to pump water throughout the system and a high-pressure pump to power the reverse osmosis process, so you need to power the pump and the entire system with electricity.

With the development and widespread application of new energy technologies, more and more new energy sources, such as solar energy, are combined with water treatment technology for water purification processes.

12. How Do You Maintain And Clean A RO Filter?

You should perform maintenance procedures to ensure your RO membrane filter works to ensure high water quality. Such procedures include:-

1) Changing The RO Filters And Reverse Osmosis Membrane.

  • Try your best to replace the reverse osmosis membrane, the post-filters, and the pre-filters periodically.
  • Replace the post-filters at least once a year and the pre-filters once every 6 to 12 months.
  • For the membrane, replace after 2-4 years if your feed water is hard and after 5-7 years if your feed water is soft.
  • Ensure that the carbon filter is in good condition because chlorine will degrade your system. You can change it every year.
  • If your feed has high chlorine content, you should consider replacing the pre-filters more frequently, i.e., six months rather than 12.
  • Also, use a TDS meter to check whether or not your RO membrane filter is in perfect working condition.

2) Draining The Reverse Osmosis Storage Tank.

You should do this once every fortnight. Draining enables the RO membrane filter to turn the stored water completely.

Do this to maintain the quality of your RO membrane filter.

3) Sanitizing The Reverse Osmosis Storage Tank

Ensure that your storage tank is sanitized every time you replace the RO membrane. Slime grows on the tanks over time.

Use a sanitizing solution to clean the tank. You can do this by running the solution through the system annually. This will remove the slime.

13. How Do You Troubleshoot A RO Filter System?

The following are common reverse osmosis membrane filter system problems and their solutions.

1) Slower Than Usual Water Flow

This problem arises from low pressure. You will notice low feed water volume.

To solve this:-

Simply check to ensure optimal water pressure, i.e., 60 PSI in the RO tank. If it is not, use a pressure gauge to raise the pressure carefully.

If the bladder in the RO tank cannot hold the pressure, you should replace the whole tank.

2) The System Running Without Stopping

This problem occurs if the check valve is broken or the shut-off valve does not close as required.

It may also arise as a result of improper membrane installation.

To solve this:-

Measure the pressure to ensure that the pressure is between 40-60 PSI.

Replace the check valve if it is broken.

3) Odor And Bad Taste

This is usually caused by stagnant water, worn-out membranes, and depleted post and pre-filters.

To solve this:-

Replace the depleted parts.

Change the storage water periodically to reduce air and bubbles. The foul odor will disappear, and your water will taste good.

4) Faucet Leakage

This occurs if the parts of your RO membrane filter are loosely fitted.

Locate the origin of the leakage.

To solve this:-

Simply drain the ports and saddle, fix the tubing, and tighten the fittings.

5) Noisy Drain Or Faucet

This is a very common problem users experience with RO membrane filters. It arises from air getting pushed out as you change filter cartridges or newly install a system.

The noise gradually reduces in under one week.

14. What Is The Price Of An RO Membrane Filter?

Figure 4 Membrane filter cartridges.

The cost ranges between $16.99 to $500 depending on the type you require. The price is worth it because of the benefits they present.

A typical RO membrane filter removes 95% of all dissolved contaminants and presents the following benefits:-

  • It is easy to install, use, clean, and maintain.
  • It reduces odor and bad taste.
  • Most importantly, it reduces harmful dissolved contaminant levels in your water.
  • It is a more environmentally friendly option than other options like bottled water.

15. What Are The Stages Involved In Reverse Osmosis Filtering?

Reverse osmosis filtering occurs in three stages. These stages are:

1) Sediment Filtration

This is the first stage in the process. Here, all suspended solids or debris, i.e., sediments that are larger than one micron, are removed.

This process is easy because, during the filtration process, these sediments will accumulate on the RO membrane surface.

2) Chlorine Removal

This is the second stage in the process. One downside of RO membrane filters is that they can be degraded by chlorine.

Therefore, chlorine has to be removed. This is done by metering reduction agents like sodium bisulfite or sodium thiosulfate upstream of the system.

An alternative way of chlorine removal is by using activated carbon filtration methods.

3) RO Membranes

This is the final stage in the process.

The membranes are 0.0001 microns in pore size.

This tiny pore size will exclude dissolved impurities and contaminants and allow water molecules to flow through.

16. Why Is Water Pressure An Important Consideration When Using RO Filters?

Water Pressure is perhaps the most important consideration when it comes to working with RO membrane filters. The water pressure is essentially responsible for flushing the rejected debris and impurities away after forcing water through the membranes.

Low water pressure could result in premature fouling and low production by the RO membrane filter. The recommended water pressure for working with an RO membrane filter is 60 PSI. If you notice pressure drops below 40 PSI, you should consider boosting it using a pump as it is insufficient.

17. How Does Water Softener Affect RO Filters?

Yes. In the entire water purification process, the water softener is a pre-filtration system that can affect the RO membrane filter by removing large particulate matter and mineral ions in the water, helping to extend the service life of the membrane.

If it is a water treatment application with a small amount of water or the water quality that needs to be treated is relatively good, such as tap water, then an RO membrane filter is enough and there is no need to equip a water softener.

18. How Do You Clean The RO Membrane?

Cleaning the RO membrane filter is simple. Impurities, debris, or scale may clog up the membrane.

You can dislodge them using chemicals to have a clean and efficient RO membrane filter.

Figure 10 Importance of RO membrane cleaning.

19. What Is The Difference Between Disinfection And Cleaning With Regard To RO Filters?

The surface of the RO membrane filter can be fouled by materials such as biological and organic matter, calcium precipitates, and metal oxide hydrates. To get rid of this fouling, you clean the membrane.

On the other hand, disinfection is done to the storage tank. The process is also known as sanitization. Ensure that your storage tank is sanitized every time you replace the RO membrane.

Slime grows on the tanks over time. Use a sanitizing solution to clean the tank. You can do this by running the solution through the system annually. This will remove the slime.

20. What Is Scaling And Fouling In Regard To RO Filters?

1) Membrane Scaling

When water is forced through the membrane, the dissolved contaminants flow into the drain. Some of these contaminants come out of the solution over time to create a thick scale.

Scale accumulates rapidly if there is insufficient water inflow into the drain and an excess flow through the membrane.

2) Membrane Fouling

This is quite similar to membrane scaling.

The only difference is that living organisms shut down the membrane by slimming like scale. In this case, the accumulation is of living organisms, not inorganic minerals.

21. How Do You Flush A RO Filter?

Flushing means getting the air out of your RO membrane filter from manufacturing.

Flushing will saturate the membranes because they are usually dried after manufacturing.

To flush it, simply put the membrane under running water or submerge it for a few minutes.

22. What Is The Cost Of Maintaining RO Filter?

To ensure peak performance of the RO membrane filters, you need to replace only the post-filters and the pre-filters.

You can do this on an annual basis. Ultimately, the frequency of use and water quality will affect how often you need to replace filters.

The RO membrane will last up to five years. On average, replacing these filters at least once every year should cost around $ 0.30 each day.

ro membrane maintenance

23. Which Factors Affect The Quality Of Water Produced By The RO Filter?

The following factors will affect the quality of water produced by the RO membrane filter:-

-RO Membrane

Different RO membranes are built for different chemical deterioration resistance, production rates, and impurity rejections.

We can supply an appropriate membrane to your process requirements to ensure filtration requirements are met.

-Total Dissolved Contaminants/Solids

The typical TDS of feed water should be lower than 500 parts per million, i.e., ppm. The amount and quality of water produced will be significantly low if the TDS exceeds this limit. You can improve the water quality by using a booster pump to increase pressure on the RO membrane.


The ideal water temperature for reverse osmosis is 76 °F or 25 °C. Also, the production will be low if the feed water is at a temperature of 40 °F or four °C or below. The high temperature will damage the membranes and, in turn, lower the quality of the produced water. Thus, we recommend purifying water with maximum temperatures of 35 °C or 95 °F.

-Water Pressure

Water quality and quantity increase with pressure. The ideal water temperature is 60 PSI. If your pressure is below this, you might consider using a booster pump. Using our RO membrane filter comes with an assurance of maintained pressure at 60 PSI throughout.

24. How Do You Store The RO Filters?

  • Store the RO membrane filters out of direct sunlight in cool areas. The temperature of the storage area should range between -5.5 °C to 45 °C.
  • Leave all-new elements or parts in their original packaging.
  • Preserve the membranes in solutions with 20% AM-225 Glycerine and 2% AM-88 preservatives.
  • Examine the preservatives frequently. If it doesn’t appear clear, remove the membrane and preserve it. Ensure that the preservative pH does not drop below 3.

25. What Types Of RO Filters Are There?

There are two common types: Cellulose Triacetate membrane filters and Thin Film Composite Filters, i.e., TFM or TCM.

The difference between these two arises from their chlorine tolerance and filtration ability. CTA membrane filters are more susceptible to fouling than TFC/TFM but are more tolerant to chlorine. They reject up to 93 percent of common impurities. TFM or TFC reject 98 percent of impurities and are not easily affected by organic fouling.

The downside to this type is that you can only use it to purify water without chlorine content. If you wish to do so, you must use a carbon pretreatment filter.

Additional Resources:

Reverse Osmosis Technology

Desalination RO System

RO Unit

RO Machine For Home

If you need any RO membrane filters, contact us now!

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