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When to change my filters?

Use this sign up form for email reminders on your RODI system

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There are 3 filters on a RODI system: a carbon, reverse osmosis (RO) and a DI filter. These all need to be changed at different times.  

Carbon: 

The carbon filter is the only filter that is more or less straight forward to replace. It can be replace by the amount of water that it has filtered. Most of the time we are unsure of the amount of gallons the system has filtered so we recommend a rough schedule by month. Sometime you might be below that mark a bit, but we still recommend replacing it unless you know 100% you have more life. We recommend replacing earlier when there is doubt as the carbon filter protects the RO filter from chlorine which can damage the RO filter. See below for the guide on each common filter size in the industry. 

A standard 2.5 in by 10" carbon filter lasts 5000 gallons

A 4.5 in by 10 in carbon filter lasts 40,000 gallons.

A 4 in by 20 in carbon filter lasts 80,000 gallons.

A 4  in by 30 in carbon filter lasts 120,000 gallons.

Reverse Osmosis (RO):

A 40 in RO membrane should last a minimum of 3-5 years when maintained.

Proper maintenance can prolong the life of the membrane past the 3-5 year mark. (see flushing the RO membrane here: link)

To test for the RO efficiency, first test the TDS at the tap before the system. Then test the RO water. Often this means disconnecting a hose right before it enters the DI filter. The water out of the RO should be around 10% of the water before the system. Take the TDS before the system and drop the last number and that is what you are looking for. EX: 357 TDS = 35 TDS goal

RO membranes only need to be replace once their efficiency drops. The goal for an RO membrane is between 85-95% efficiency. This means 85-95% of the TDS is removed by the RO. Another way to look at this is the remains TDS after the RO filter should be between 5-15% of incoming TDS from the tap. EX: 250 TDS at the tap should be about 10% after the RO, which is 25. SO an ideal range is 15-30 - ish. Once it falls to about 80% or lower efficiency we recommend replacing. EX 250 TDS at 80% efficiency, or 20% remaining, is 50 TDS after the RO.

DI Filter:

DI filters are perhaps the hardest to determine when to replace before it is time to replace. This is because there are a lot of moving parts in DI filter life.

Water quality is a huge factor in DI filter life. Even in the same service area a DI filter life can last 2x as long, or 2x shorter, due to water variances around the city.

How often the system is used is also a factor in DI filter life. The more often it is used the faster the DI resin will be used up.

The only true way to know is by testing the TDS. Once TDS is over 0 ppm, its time to think about replacing. Once the TDS is over 7 ppm is is definitely time to replace or the water will start to spot.

A 10 inch DI filter can last around 1 month.

A 20 inch DI filter can last around 2 months.

A 30 inch DI filters can last around 3-6 months.

Of course, any of these filters can last much shorter, or perhaps a bit longer than the typical life expectancy.


How to sign up for automated email reminders:


Use the popup form that appears on this page only to sign up for automated emails that remind you when its about time to change your filters. The pop up form should appear within one minute of loading this page, or by the time you scroll all the way to the bottom. (If it has not loaded, try reloading the page or opening in a private or incognito page)


These emails will come automatically and will be based on when the date you enter into the field when you signup. A good date to use is the day you purchased your system, or the date you last changed your system, or the date you will next change your filters. 

These emails are based on typical filter consumption.

Select the system you have from us and they emails will match the the filters you have. If you have more than one system, you can select multiple. 


This email list will ONLY send emails related to filter changes. You won't receive any of our marketing or promotion emails. If you want to sign up for promotion emails, use the signup form on the bottom of every page.