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How Often Should I Change My RO Filters?

by Mark Timmons November 23, 2014 21 Comments

John asks:

I have a water softener and a pre-filter ahead of my Reverse Osmosis System. How often should I change the filters?

The Water Doctor replied: Water quality varies so much that it is impossible to give you an accurate answer. For example, some water is more turbid and contains more solids. Water that looks substantially the same could plug a filter in a month... or a year. The thing is, you don't want to wait until the filter is plugged, you want to changed it before solids or chlorine comes through. On hard water, I have seen membranes last six months to a year and on soft water, they can easily last three to five years.

In my own personal case, I have one of THESE in my home. I test the water hardness and chlorine levels on a weekly basis and these the RO for TDS levels multiple times a week. The only way you can know if your membrane needs changed is by testing the TDS and when it drops to below 80% rejection, it is time to change it. By testing the softness of the water, you can know how well it is working and adjust it to meet your needs. In many cases you can change the RO Filters on a yearly basis, if you have soft water and proper pre-filtration, but it never hurts to do it more often. After all, this is your drinking water we are talking about.

For whole-house filtration, the absolute best filtration is a 5 micron "Pleated" filter like THIS. At the very minimum, if you have a water softener, you should at least have a test kit to test the hardness, like this: Hardness Iron & PH Field Analysis Water Test Kit It is good for 50 tests, so if you test your water once a week, it will last a year and then the testing chemicals can be replenished HERE. The professional grade test kit includes tests for pH, iron, chlorine and TDS, but you can also buy a TDS meter HERE. Everyone that has a reverse osmosis system should have a TDS meter and this is a professional-grade model that lasts for years. You wouldn't dream of having a furnace or air conditioner without a thermostat - why on earth would you have a reverse osmosis system without a TDS meter? Think about that! Here is the LINK to all of our water testing products.

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April 04, 2018 Ross Welburn

I’m on a well and use a water softener. The Softened water is 66ppm and the RO water is 7ppm. The RO membrane is 15 years old. We have no chlorine in our water, I just dont like the taste of softened water. Is those reasonable numbers? Tks, Ross

June 24, 2018 Melani Wendling

Could a person get sick on the water if the filters aren’t changed?

June 24, 2018 Mark Timmons

What kind of RO do you have?

January 17, 2019 Mark Timmons

Thank you – it works now.

January 17, 2019 Mark Timmons

1. Membrane is not pushed all the way in;
2. Bad membrane; or
3. If it is a permeate pump system, you have TDS creep.

April 09, 2019 Mark Timmons

The TDS has little to do with changing filters, although if you don;t change the filters at appropriate intervals, the membrane will be damaged due to sediment or chlorine.

Filters should be changed at least once a year… Every 6 months if the water is really bad.
The TDS is what the membrane reduces and you need a TDS Meter to determine how well the membrane is working:

April 12, 2019 Mark Timmons

Those are good numbers but I would replace the membrane and filters. Hetrotrophic bacteria are a problem in an RO System. You can use this as a final filter to kill bacteria:

July 15, 2019 Mark Timmons

Yes, it is certainly possible.

July 18, 2019 Mark Timmons

I always suggest once a year.

April 09, 2020 tony

I have a 1/2 micron whole house filter that goes into a Water Softener then into 5 micron filter under the sink then the 4 stage RO system. How often should I change out the 4 stage filters?

April 09, 2020 Jack

My new R/O system professionally installed 4 1/2 months ago slowed to one drop per second. It’s a 50 gallon per day 1:1 ratio system. Two weeks ago the installer came back and replaced the membrane. The output went back to about 2 gallons per hour. Now, two weeks later, it’s down to a little over a gallon per hour. I’m using city water which my TDS measures around 473. The R/O water measures 23 and hasn’t changed since the membrane is replaced. Using the same TDS meter, I’ve also measure the water from a vendor with industrial capacity R/O system with reading of 2. Obviously the vended water is purer, but this gives me confidence in the TDS readings.
What can cause the water output to slow so quickly? Are there some specific things in the water I can test for to narrow down the cause of the problem?

June 23, 2020 Nancy ferraro

Have well water in recently purchased home. Never had a well before. 3 step system under the kitchen sink. Want to change filters. Is the water safe to drink with this system? Do have a water softening system.

July 04, 2020 Mark Timmons

t is simply good practice to change them out once a year.

November 23, 2020 Mark Timmons

It sounds like a water quality issue. Poor water quality can plug a RO Membrane quickly. It could also be a problem with the flow control (plugged or too small).

December 01, 2020 Mark Timmons

I would recommend a detailed water test before I could make that determination.

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