How to Change Reverse Osmosis Filters + Replace the RO Membrane

Written by: Gene Fitzgerald // Last Updated: Mar 7, 2023

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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? Time to replace RO filters!

Contents

Reverse osmosis filter replacement schedule: How often & when to change
How to replace reverse osmosis filters (including an inline post-filter)
Replacing the RO membrane
Where to buy reverse osmosis filters and membranes
How much do replacement filter elements cost?

Key Takeaways

Here is how to replace the filters and membrane of a reverse osmosis system:

Wash your hands to prevent contaminating your new filter elements.
Turn off the water supply and close the storage tank valve.
Open the RO faucet to depressurize the system and drain any remaining water.
Unscrew the pre-filter housings and clean their insides with warm dishwater if need be. You can also use unscented household bleach or another suitable sanitizer. Rinse thoroughly afterward.
Install the new pre-filters and also change the post-filter, if needed.
Open the RO membrane housing and take out the old membrane. Clean/sanitize the housing if needed and don’t forget to rinse.
Push the new membrane into the housing all the way in until it’s seated tight. Close the cap.
Turn the water supply back on, open the RO tank valve, open the RO faucet, and let the system flush for a couple of minutes. Check for leaks.
Close the faucet and let the tank fill. Discard 1 or 2 full tanks of water before use.

Reverse Osmosis Filter Replacement Schedule: How Often & When to Change

We get it, you don’t want to replace your reverse osmosis filters too often and waste money, but you also don’t want to leave them in for too long putting your health at risk. No worries, simply follow this RO filter replacement schedule to be on the save side:

Biannual Replacement	Annual Replacement	Every 3 to 5 Years
Sediment and carbon pre-filters	Sediment and carbon pre-filters
	Carbon post-filter
		RO membrane

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.

Why Should You Change Your Reverse Osmosis Filters?

Failing to change filter elements 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.

How Often to Replace 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.

Sediment pre-filters in a reverse osmosis system should be replaced every 6-12 months.

How Often to Replace 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 pre-filters in a reverse osmosis system should be replaced every 6-12 months.

How Often to Replace the 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.

You should change your carbon post-filter every 12 months.

When to Replace the RO Membrane (+ Testing for a Bad RO Membrane)

The easiest and safest method to determine if your RO 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 so.

How to Replace Reverse Osmosis Filters (Including an Inline Post-Filter)

So, how to change reverse osmosis filters?

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.

Start by washing your hands – you don’t want to contaminate your new filters.
Turn off the water supply.
Close the storage tank valve.
Open the RO faucet to depressurize the system and drain any remaining water. Once the dripping stops, close the faucet.
Place a bowl underneath the system.
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.
Clean the inside of the housing(s) with warm dishwater if need be. If you want to sanitize your RO system use unscented household bleach or another suitable sanitizer. Rinse thoroughly afterwards.
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!
To change the inline 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.
Turn the water supply back on.
Open the RO tank valve.
Open the filtered water dispenser and let the system flush for a couple of minutes.
Check for leaks.
Close the faucet and let the tank fill.
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.

Further Reading:

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.

Replacing the RO Membrane

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…

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

Again, start by washing your hands.
Turn off the water supply.
Close the storage tank valve.
Open the RO faucet to depressurize the system and drain any remaining water. Once the dripping stops, close the faucet.
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.
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.
Take out the old membrane. If it doesn’t move use needle-nose pliers.
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. Rinse thoroughly afterwards.
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.
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!
Reconnect the membrane by pushing the tubing into the cap fitting. Pull back on the tubing to ensure a secure connection.
Turn the water supply back on.
Open the RO tank valve.
Open the filtered water dispenser and let the system flush for a couple of minutes.
Check for leaks.
Close the faucet and let the tank fill.
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.

Where to Buy Reverse Osmosis Filters and Membranes

Like purchasing reverse osmosis systems, replacement filters and membranes can be purchased from several sources.

Generally speaking though, you’re better off purchasing the replacement filters directly from the same manufacturer that you purchased the system from. While aftermarket filters can work for systems with standard-sized cartridges, you’re not guaranteed the same level of contaminant removal. Aftermarket filters can often be purchased for less than the cost of the original filters, but again you don’t know exactly what you’re getting unless they’re NSF certified.

Direct from Manufacturer

As mentioned previously, the best option is usually to purchase directly from the RO system manufacturer. That way you know you’re getting the exact replacement filters you need, and you won’t have any warranty issues should you run into trouble with anything.

Online Retailer

Another option is purchasing replacements from a large online retailer. These retailers typically have large product selections, so there’s a good chance you’ll find your brand’s filters available.

If you’re willing to take a gamble with aftermarket replacement filters, then a large online retailer is the way to go. They typically have the cheapest prices, offer discounts, and you’ll be able to return anything if it doesn’t suit your needs.

Local Water Treatment Expert

If you have a local water treatment supplier, they may have what you need available, but keep in mind you’ll likely pay more than you would when purchasing from an online retailer.

Hardware Store

Hardware stores may also have replacement filters available, and they generally offer a good blend of price and availability. Returns are also easy should you have any compatibility issues.

How Much Do Replacement Filter Elements Cost?

Replacement filter costs will vary depending on the filter quality, brand name, and the specific filter element you need.

Generally speaking though, pre and post-filters will run you between $10 on the low end to $50 on the high end. RO membrane replacements cost between $25 on the low end and $100 on the high end.

You can also purchase filter replacement sets that have all of the required pre and post-filters – including the RO membrane – for less than the cost of purchasing each one separately.

If you have any questions about how to replace RO filters please don’t hesitate to leave a comment below!

About the Author Gene Fitzgerald

Gene Fitzgerald has been with BOS since the very beginning. She is head of content creation and has fully immersed herself into the home water treatment industry only to become an expert herself. Outside of BOS, Gene loves reading books on philosophy & social issues, making music, and hiking.
Learn more about Gene and the rest of the BOS Team.