Reverse Osmosis Filter Replacement | How to Change an RO Membrane

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Changing the RO membrane on your reverse osmosis system is essential for having clean, filtered water. If you are serving or drinking RO water daily, it’s important to change the filter every 6-12 months, depending on how hard your water is. Replacing your RO membrane takes less than ten minutes and is not very expensive (~$20). The most common reason people do not often replace their filters is that they forget when they last did it, which leads to low-quality tap/well water and, therefore, bad-tasting coffee and tea! I hope this article will serve as a helpful reminder for those who have had their units for over 18 months (the time period recommended by the manufacturer) and those who are new to using RO systems or have had their units for less than 6 months.

We will also show you how to change your sediment filter, carbon filter cartridge, and membrane housing O-Ring gasket if needed.

How to Replace Reverse Osmosis Filters

1. Remove the faucet to access the membrane housing (usually requires loosening a screw underneath the sink but could require completely removing your faucet).

2. Remove any hoses or tubes connected to the membrane housing (see pictures)

3. Once you’ve removed everything attached to your RO membrane housing, it should slide right out for you to access the inside! The old membrane will be on either side of the centrepiece that holds your filter canister in place – remove both membranes and set them aside. There may also be two small filters attached – these are the sediment filter and carbon filter; they can usually just be slid out as well (if not, see next step). 

4. Once you have removed both membranes, the old sediment filter and the old carbon filter – it’s time to install your new ones! Reverse osmosis systems usually come with a sediment and carbon pre-filter that should be replaced approximately every 6 months or 150 gallons of usage. The membrane can last about 18 months before needing replacement (depending on water quality). The other two filters should be replaced at the same interval if they are clogged. It’s a good idea to write down when you change each component, so you don’t forget!

5. Now slide the membrane housing back into place along with your intake line from your RO unit, as well as any hoses needed to deliver your water to your faucet. You should then add your filters, reattach everything you previously had disconnected from the membrane housing, and you’re all finished!

6. Run a few gallons of water through your RO system to flush out any remaining old water in the unit and ensure no leaks or issues with pressure after installing a new membrane filter. This will also help get rid of any bad taste from the old filters… but if not, continue to step 7…

7. If you would like an alternative option for getting rid of old filter flavours, try adding one drop per gallon (or litre) directly into the empty tank before running it through; this helps reduce tastes/smells significant.

8. If you are extremely sensitive to tastes or smells, I recommend running double the amount of water through your unit (as described in step 6) and then adding one drop per gallon/litre directly into your tank(s) after rinsing out any remaining filter smells. Then you should be good to go!

If there is no TDS meter available, this method can also help determine when to change valves: When the membrane has not been replaced in over 18 months, the membrane starts to break down and therefore see the reduced output. As this happens, more contaminants get through the RO system because of reduced output, thus increasing TDS readings (because they are getting through unfiltered). I suggest testing your TDS readings on your water before putting it through the RO unit and after (on the same number of gallons) to determine when it’s time for a new membrane.

Replacing Modular System Filters

It’s much easier to replace modular filters. There is no need to turn off the water supply or relieve pressure. Place a bowl under the system, twist off the old filters, and replace them with new ones.

Frequency: How Often to Change

We understand that you don’t want to replace filters too often, wasting money, but you also don’t want to leave them in for an extended time, putting your safety at risk. What’s most essential is that you replace the filters regularly. It’s the only way to ensure consistent water quality. The frequency with which you change them depends on two factors:

  • The condition of your feed water –The pre-filter must be cleaned or replaced regularly to minimize the buildup of sediments and hardness minerals in it, as this will significantly reduce its lifespan.
  • How much water you consume – It’s good to know that the filters will last for about three months.

A good mix of dirt and carbon pre-filters, on the other hand, should last between 6 and 12 months. A carbon post-filter is generally adequate for 12 months, although some may survive up to 2 years.

Please keep in mind that these are only rough guidelines. Especially low-cost aftermarket filters might need to be replaced more often. Also, if you’re buying from a different source, double-check that the quality is up to snuff – look for NSF certifications.

Failing to change filters promptly will

  • Reduce the overall purity of the permeate water. Favorable growth and accumulation of waterborne germs (fouling) in the filtering system can have negative health consequences and contribute to an unpleasant taste and odor to your water.
  • Reduce water flow and pressure. In the long run, increased wastewater production results in a higher water bill.

RO Membrane Replacement

What is the easiest way to keep a reverse osmosis membrane in good condition? Cleaning and appropriate feed water treatment are first and foremost. Even with the most thorough cleaning procedure and best feed water treatment, every RO membrane must be replaced…

How to Replace

  1. Again, start by washing your hands.
  2. Turn off the water supply.
  3. Close the storage tank valve.
  4. Turn off the RO faucet to depressurize the system and drain any remaining water. Close the faucet when the dripping has stopped.
  5. Remove the water line from the membrane cap. To withdraw the tubing, push in and hold down the collet against the fast connect fitting. You may also need to remove a plastic clasp.
  6. Remove the cap by rotating it counterclockwise. You may need a filter wrench or a strap wrench for this. It’s also a good idea to have a towel on hand if water spills.
  7. Remove the old membrane. If it doesn’t budge, needle-nose pliers can help. If necessary, clean the membrane housing inside with warm dishwater. Household bleach or another suitable sanitizer may be used for disinfection if unscented household bleach isn’t available. Afterward, rinse thoroughly.
  8. Push the new membrane into the housing until it is fully seated. The end with the two black O-rings goes in first. Try to avoid touching the membrane with your bare hands to prevent infection.
  9. Before reassembling the housing cap, double-check that the black rubber O-ring is secure and in good working order. If necessary, replace or lubricate with silicone grease. Use a wrench to tighten the cap gently but firmly!
  10. Using a screwdriver, carefully pry up the membrane and fix it back in place. Push the tubing into the cap fitting with your hands. To verify a secure link, pull on the tube.
  11. Turn the water supply back on.
  12. Open the RO tank valve.
  13. Open the filtered water dispenser and let the system flush for a couple of minutes.
  14. Check for leaks.
  15. Close the faucet and let the tank fill.
  16. Before you begin, fill 2 or 3 full tanks with water and discard 1 or 2 full containers. This is to remove the preservative from the membrane after flushing. If the water still has an odd flavour/odor after two flushing sessions, keep on doing so.

When to Replace

The simplest and safest method to tell whether your membrane needs to be replaced is measuring the TDS of permeate water (Total Dissolved Solids). This can be done with a TDS meter. To calculate the TDS rejection rate, use the following formula:

Rejection rate in % = (TDS of untreated tap water – TDS of purified RO water) / TDS of untreated tap water x 100

If the rejection rate falls below 80%, it’s time to replace the membrane. Reduced water flows from the faucet is another sign of a worn-out membrane.

How Long Does an RO Membrane Last?

Reverse osmosis membranes, made with state-of-the-art technology, generally last 3 to 5 years if you replace pre-filters on schedule. If your well water is highly contaminated, a new membrane may be required every year or every other year.

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