How Long Do Water Filters Last?
Probably you have seen an ad for a small, one-cartridge “ten stage” water filter that promises to remove chlorine, lead, pesticides, herbicides, VOCs, fluoride, and “pharmaceuticals,” and to “last for 10,000 gallons.” This advertising claim is actually true. But at the same time, it is a big lie. A really big lie.
The intent is to imply that the filter will remove fluoride, VOCs, and all the other heavy contaminants listed “for 10,000 gallons.” But what “lasts for 10,000 gallons” really means is that it won’t fall apart and that it may even be removing some chlorine after 10,000 gallons. While it may “remove fluoride” for the first few gallons, it really doesn’t contain enough fluoride media to last past the original cartridge rinse. The trick is in the words. It’s true that it “removes fluoride” and that it “lasts for 10,000 gallons,” but it certainly doesn’t remove fluoride for 10,000 gallons.
Even single media filters, like carbon blocks, have greatly different capacities for various contaminants that they treat. Filter carbon is a very effective treatment–the best, in most cases–for a large majority of water contaminants, but in almost every case carbon filters treat chlorine much longer than they effectively treat more difficult contaminants.
For example, the manufacturer of one superb carbon block filter states the capacity of its 2.5″ X 10″ cartridge for removing chlorine as 20,000 gallons @ 1 gallon per minute. For removal of VOCs, however, the claim is for only 500 gallons at the reduced flow rate of 0.5 gallons per minute.
It is a mistake to assume, in other words, that the filter will remove VOCs as long as it will treat chlorine. If chlorine removal and taste/odor improvement are the only goals, then the filter can be used to its full chlorine capacity; but if you really need serious removal of specific contaminants, you should find out the cartridge’s capacity for the specific item you’re targeting and change the cartridge accordingly.
You should also notice that flow rate matters–a lot–and that if you want a faster flow rate, you need a larger filter.