RO filter replacement

Reverse Osmosis Filter Replacement 101 + How to Change an RO Membrane

Changing the filters and the membrane of your reverse osmosis system on a regular basis is key if you want great tasting drinking water that is clean and healthy.

And the good news is that it can be done by the average Joe with zero plumbing experience. All you need are some basic supplies and a little bit of patience.

Ready to get started? Let’s go!

Contents:

RO Filter Replacement

How to Replace Reverse Osmosis Filters

So, how can you replace the filters of your reverse osmosis system?

Although every model is a bit different, here are some basic steps that apply to most RO units:

Before you start, you should check the product manual. It most likely includes detailed instructions that outline the filter replacement procedure for your specific system.

  1. Start by washing your hands – you don’t want to contaminate your new filters.
  2. Turn off the water supply.
  3. Close the storage tank valve.
  4. Open the RO faucet to depressurize the system and drain any remaining water. Once the dripping stops, close the faucet.
  5. Place a bowl underneath the system.
  6. Remove the housing of the pre-filter(s) that you want to replace by turning clockwise. You might need a filter wrench or strap wrench for this. It also makes sense to have a towel at the ready in case of spilling water. A bucket comes in handy to place the old filters in.
  7. Clean the inside of the housing(s) with warm dishwater if need be. If you want to sanitize your system use unscented household bleach or another suitable sanitizer. Rinse thoroughly afterwards.
  8. Install the new pre-filter(s). In order to prevent leaks, make sure that all black rubber O-rings are in place and in good condition before screwing the housing(s) back on – replace and/or lubricate with silicone grease if need be. Feel free to use a wrench to tighten the housings, but be careful not to overtighten!
  9. To change the post-filter, push in and hold down the collet against the quick connect fitting to pull out the tubing. Repeat on other end. Remove the cartridge and install replacement (check arrow for flow direction). Reconnect the filter by simply pushing the tubing into the fitting on each side. Pull back on the tubing to ensure a secure connection.
  10. Turn the water supply back on.
  11. Open the RO tank valve.
  12. Open the filtered water dispenser and let the system flush for a couple of minutes.
  13. Check for leaks.
  14. Close the faucet and let the tank fill.
  15. If you have changed the post-filter you should discard 1 or 2 full tanks of water before use. Discolored water may come out of the faucet at first. This is nothing to worry about. It’s just the carbon fines being flushed out and should clear out after the first or second flush.

Finally, write down the date of the filter replacement as guidance for the next. Also, if your RO faucet comes with a filter change indicator remember to change the battery.

Video

Eric from emoneyblue has done a great job demonstrating how to replace RO system filters (+ the membrane) in a matter of minutes:

Replacing Modular System Filters

Replacing modular filters is much more convenient. There is no need to turn off the feed water nor to release pressure. Simply place a bowl underneath the system, twist off the old filters and install the new. Don’t forget to check for leaks! That’s all.

Our favorite modular RO system? The Home Master TMAFC.

Frequency: How Often to Change

We get it, you don’t want to replace filters too often and waste money, but you also don’t want to leave them in for too long putting your health at risk.

What’s most important is that you change on a regular basis. It’s the only way to guarantee consistent water quality. How often primarily depends on 2 factors:

  • The condition of your feed water – High levels of sediment or hardness minerals, for example, will lower pre-filter lifespans significantly.
  • How much water you consume – The more water you use for drinking and cooking, the sooner the filters will reach their capacity limit.

That being said, regular sediment and carbon pre-filters should last between 6 and 12 months. A carbon post-filter is usually good for 12 months, although some may last up to 2 years.

Please consider these as general guidelines. Especially cheap aftermarket filters might require more frequent replacements.

By the way, if you are going to buy from another source make sure that the quality is up to standards – think NSF certifications.

filter cartridges

Failing to change filters in a timely manner will

  • Decrease the overall purity of the permeate water.
  • Favor the accumulation and growth of waterborne pathogens (fouling) in the filtration system which can affect your health and add an unpleasant taste and smell to your water.
  • Lead to a drop in output water flow and pressure.
  • Cause increased wastewater production which ultimately leads to a higher water bill.

All four are indicators that a filter replacement is probably overdue.

Sediment Pre-Filters

Sediment pre-filters are found in stage 1, sometimes stage 1 + 2, of almost all RO under sink filter systems on the market. They trap rust, sand, silt and other debris to protect the delicate reverse osmosis membrane at the heart of the system from premature clogging.

Carbon Pre-Filters

Carbon pre-filters are found in stage 2 (and 3). The cartridges contain activated or catalytic carbon in granular or block form. The filters are most effective at removing chemicals including chlorine plus its disinfection byproducts and VOCs which would otherwise damage the RO membrane. They are also great to eliminate tastes and odors.

Carbon Post-Filter

Carbon post-filters come into play at filter stage 4 or 5 and give your water a finishing touch. They are mainly used to remove residual tastes and odors that might have leached into the water while in the storage tank.

RO Membrane Replacement

Lead, fluoride, bacteria – a reverse osmosis membrane that is in good condition removes up to 99% of all water contaminants.

How to keep a membrane in good shape? First and foremost, through regular cleaning and appropriate pre-treatment of the feed water.

However, even with the most thorough cleaning procedure and the best pre-treatment in place, every RO membrane has to be replaced eventually…

RO membrane

How to Replace

Before you start, you should check the product manual. It most likely includes detailed instructions explaining how to change the membrane on your specific system.

  1. Again, start by washing your hands.
  2. Turn off the water supply.
  3. Close the storage tank valve.
  4. Open the RO faucet to depressurize the system and drain any remaining water. Once the dripping stops, close the faucet.
  5. Remove the water line from the membrane housing cap. Push in and hold down the collet against the quick connect fitting to pull out the tubing. You might also need to remove a plastic clip.
  6. Remove the cap by turning clockwise. You might need a filter wrench or strap wrench for this. It also makes sense to have a towel at the ready in case of spilling water.
  7. Take out the old membrane. If it doesn’t move use needle-nose pliers.
  8. Clean the inside of the membrane housing with warm dishwater if need be. Unscented household bleach or another suitable sanitizer can be used for disinfection (more info here). Rinse thoroughly afterwards.
  9. Push the new membrane into the housing all the way in until it’s seated tight. The end with the 2 black O-rings goes in first. Tip: Try to avoid touching the membrane with your bare hands to prevent contamination.
  10. Double-check that the black rubber O-ring sits tight and is in good condition before screwing the housing cap back on – replace and/or lubricate with silicone grease if need be. Feel free to use a wrench to tighten the cap, but be careful not to overtighten!
  11. Reconnect the membrane by pushing the tubing into the cap fitting. Pull back on the tubing to ensure a secure connection.
  12. Turn the water supply back on.
  13. Open the RO tank valve.
  14. Open the filtered water dispenser and let the system flush for a couple of minutes.
  15. Check for leaks.
  16. Close the faucet and let the tank fill.
  17. Discard 1 or 2 full tanks of water before use. This is to flush out the preservative inside the membrane. In case the water still has a funny taste/smell to it after 2 rounds, keep flushing.

As with the filter replacement, it is helpful to write down today’s date as guidance for when to change the membrane next.

When to Replace

The easiest and safest method to determine if your membrane needs changing is by measuring permeate water TDS (Total Dissolved Solids). This can be done with a TDS meter.

First, test the TDS of the untreated tap water. Then test the purified RO water.

You can calculate the TDS rejection rate by using 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 drops below 80 percent it is time for a replacement.

Another indicator for a worn-out membrane is reduced water flow from the faucet.

How Long Does an RO Membrane Last?

State-of-the-art reverse osmosis membranes usually last for 3 to 5 years, provided that you replace pre-filters according to schedule. If you are on well water and the contamination is particularly bad a new membrane might be required every year or every other year.

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If you have any questions about how to replace the filters or membrane of a reverse osmosis system please don’t hesitate to leave a comment below!

Leave a Comment:

1 comment
Ray says 3 weeks ago

I calculated my rejection rate to 4% after replacing previous filter, post filter and cta ro membrane. I then completely drained the bladder tank and the rejection increased to 5 %.

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