How often will I need to change the shower filter cartridge?
Seems like a simple question. Which shower filter do you have? Which cartridge does it take? Lookup the answer. Done.
Unfortunately, the interval for cartridge replacement is only an exact science under laboratory conditions.
Here are a few variables that can effect shower cartridge life:
- Number of showers per day
- Length of each shower
- Quantity and type of dissolved solids in the water
- Sensitivity of the individuals using the shower
Let’s Get a Ball Park Number…
For an estimate, start with the NSF 177 rating of the shower filter. Let’s use the Sprite High Output number, which is 10,000 to make the math easy.
The standard flow rate for shower heads is 2.5 gallons per minute.
If you have two people that take a 10 minute shower every day, that would be 50 gallons per day (2 x 10 x 2.5 = 50 gallons).
Just divide 10,000 gallons by the gallons used per day to get an estimated cartridge life in days (10,000 / 50 = 200 days).
Now for the differences in water…
NSF 177 testing is done with water that has total dissolved solids in a very specific range. This keeps the tests results consistent from one test to the next, so we can compare different models tested at different times.
Well, odds are, your water is different from the water used in NSF testing. It probably has more or fewer dissolved solids, so your cartridges would be consumed more quickly, or last longer, respectively.
To account for this, you should just replace your cartridge at the recommended interval or the one you calculated above and note whether there is a huge difference after you change the cartridge.
One other difference you might notice in extreme cases is reduced flow through the shower filter. If you notice reduced flow, it’s probably time to change the cartridge.
If you notice a really big improvement in your shower after replacing the cartridge, you should probably replace it a couple of weeks earlier next time.
You can mark this on your calendar to track it if you’re the real exacting type. 
Now for the personal differences…
Some of us are more sensitive to the effects of chlorine and hard water than others. If you’re very sensitive to chlorine, you might notice a big difference when changing a cartridge at the estimated age.
Someone who is less sensitive to chlorine might not notice a difference at all when the shower cartridge is left for a longer period.
Shower cartridges are consumed gradually, by each gallon of water that flows through them. Since it’s a gradual process, you might not even notice the change until you replace the cartridge.
So start with the recommended interval for changing your shower filter cartridge and see how different the water feels. If it’s a significant difference, just replace the cartridge a couple of weeks earlier the next time around.
Naturally, if you got a shower filter to relieve asthma irritation from chlorine inhalation or to ease a skin condition like eczema, try replacing the cartridge if your symptoms return before the standard replacement interval.
If you’re not sure which shower filter cartridge fits your filter, check out our handy page with pictures to help you find the right one. If you’re still not sure, there’s a place to ask a question and get some help.