When Should You Change The Filters On A Reverse Osmosis Water System?

There are different answers and opinions about when RO filters and membranes should be changed.  3-stage RO filters use CTA membranes and 4 and 5-stage RO filters use thin film membranes.  Thin film membranes last longer and produce purer water than CTA membranes.

RO filters using CTA membranes should have the filters and membrane changed every year or when the RO filter begins to produce 200ppm water, whichever comes first.  Most often the 3-stage RO filter system will be producing less than 200ppm water in one year.  With new filters and a new membrane a 3-stage RO filter will produce somewhere between 40ppm and 90ppm water depending on how soon after being manufactured the CTA membrane is installed.  As time goes by the ppm count will slowly but steadily increase due to the membrane losing its efficiency.

RO filters using thin film membranes should have the filters and membrane changed every eighteen months or when the RO filter begins to produce 100ppm water, whichever comes first.  Most often the 4 and 5-stage RO filters will be producing less than 100ppm water in eighteen months.  With new filters and a new membrane the 4 and 5-stage RO filters will produce somewhere between 10ppm and 40ppm.  As time goes by the ppm count will slowly but steadily increase due to the membrane losing its efficiency.

To put the ppm numbers in perspective, the most popular bottled water measures between 50ppm and 200ppm.  It is very likely that a 5-stage RO filter will produce water that measures less than 50ppm for the full eighteen months.  In other words, if a 5-stage RO filter is maintained as suggested, it will produce higher quality water for the whole eighteen months than bottled water.

The only readily available water that is more pure than 5-stage RO water is distilled water.  The reason distilled water is not more popular for drinking is that most people prefer the taste of RO water.

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