When You Should You Change Reverse Osmosis Filters

Posted by Janice Macdonald on

Confused about how often or when you should replace water filters?

Let's break it down and hopefully shed some light on this important question. After all, you bought a water purifier because you wanted pure water, so proper maintenance and filter changes will help you achieve that end.

Most reverse osmosis drinking water systems are the same (they just look different)

Most reverse osmosis units have 3 lower filter sumps. These sumps usually contain 1 sediment filter and 2 carbon filters and a membrane across the top. Some have an extra polishing filter also across the top.



 The easiest and most economical systems to maintain have 3 lower filters and a membrane on top. If space is an issue and the unit is installed under the sink, sometimes you will have 2 lower filters, a membrane and polishing filter on top. This just uses less space.


Reverse osmosis systems work this way

First your water should be soft, either naturally or by means of a water softener. Then the water passes through a sediment filter, followed by a carbon filter. The next stage is the membrane. From here the water goes to a storage tank. When you open the faucet, the water is released from the tank then passes through a polishing carbon filter for taste and odour.

There are some variations on this theme, such as an added calcite filter to alkalize the water, but that’s the basic idea. A few systems have proprietary filters that twist on. Those would include Culligan, Vectapure, Freshpoint and Aqua Flow (previously know as Pura) Canature, Ecowater and a few others. Twist filters are generally more expensive and should be changed yearly. Membranes should be changed every 3-5 years.

If you live in a BIG city all your reverse osmosis filters should be changed more often

The larger the city, the more likely you are to have chloramines added to your water by the municipality to treat bacteria. Chloramines contain chlorine and ammonia. 

While you want to remove all chemicals from your drinking water, chloramines are especially difficult to remove and your carbon filters will have to work hard to do the job. So, change your reverse osmosis filters every 6 months to 1 year.

Some small cities and towns still use free chlorine to treat the water

If your water is treated with free chlorine your carbon filters will last a little longer, so for most families a yearly change will do the trick. If in doubt, check with your local municipality or just change your filters more often—no harm in that.

If your water comes from a private well you should change your sediment filter more often

You will probably have some iron and possibly sediment in your water. You should change your sediment filter every 3-6 months and your carbon filters every 6-12 months at least. Carbon filters are mainly for chemical removal, so if you don’t chlorinate your well, they will last much longer than the sediment filter.

Reverse Osmosis manuals can't tell the whole story about when to change your water filters

The manual that comes with your system is about the system. It's not about YOUR water specifically. It can't tell you how often to change your filters as it doesn't know where you live. It's that simple.

When in doubt, change your reverse osmosis filters and membrane more often

If you notice an odour or if your water is discolored then the first thing to do is change the filters and membrane. If you neglect your water system it will produce water less palatable than tap water.  

What about all those extra filters on top?

If you got talked into buying a system with a lot of extra filters, you can probably change the extra polishing filters less often than the 3 lower filters without sacrificing water quality. That's because the water moves through these filters AFTER passing through the membrane, which is the filter doing all the work. The water is purified before it gets to all those extra filters.


What about Ultra Violet on a reverse osmosis?

U.V. attachments on RO systems are sometimes useful on well water, but if you are on a well and have bacteria, it's much safer to treat the whole house. If you are on city treated water, your local water department adds enough chlorine and ammonia to treat bacteria outbreaks. 

How often should I change my reverse osmosis membrane?

Membranes vary and can be either encapsulated or can fit inside a membrane housing. On twist filter systems the membrane looks much like another vertical filter.

How often you change the membrane should be determined by three things; how soft your water is, how much water you use, and how much chlorine and ammonia is in your local water supply.

Soft water will protect the membrane from calcium build up and is recommended. High levels of Chloramine will damage the membrane unless your carbon filters are changed regularly. If you produce a lot of drinking water then the membrane will not last as long. 

If you own a total dissolved solids meter (TDS Meter) then you can check your own water quality. 

The TDS reading of your water will give you clues as to when you should change your membrane. It can't test for filter performance as it doesn't test for chemicals but it can tell you when the total dissolved solids number is creeping up. Again, every area will be different as the total number depends on the freshness of the membrane combined with the TDS starting number. Look for numbers between 50ppm and 100ppm. In hard water areas where some calcium passes through the membrane you might have slightly higher numbers. It's not about the number specifically as it's a rejection rate. 

Can't remember when to change your water filters?

If you don't change your filters regularly your reverse osmosis membrane will suffer and eventually your water quality will be poor. You can sign up for no commitment reminders when you purchase filters from Ontariosoftwater.ca. It's just a reminder, your credit card won't be billed and you still have to finalize the purchase if you decide to buy more filters. It's convenient and absolutely commitment free.


Do you have more questions about when to change your reverse osmosis filters?

There are a lot of different systems out there. If you aren't sure about yours, we invite you to send a picture of your reverse osmosis unit and your question to sales@ontariosoftwater.ca 

We've been selling water filters all over Canada for over 25 years! 


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