Many viruses and microorganisms are also non-absorptive, or too small to be filtered by activated carbon. To rid a water source of these, the Water Quality Association recommends chemical or other kinds of non-carbon filtration. As any camper knows, halogens such as chlorine and iodine will easily deal with protozoa, while common home filter choices are ultraviolet (UV) light and reverse osmosis mechanisms.
As a general rule, if it’s an organic compound, it contains carbon. Therefore, it’s potentially filterable by activated carbon (depending on the compound’s size, and the filter’s ability). If the material is inorganic or non-carbon-based, then a carbon filter will not remove it through adsorption—but, the may filter still work, simply as a result of its ability to strain out particulates.
But my carbon filter says it’s certified for lead/non-organic compounds?
Some manufacturers do use various blends and add-ons to turn activated carbon into a material capable of advanced contaminant reduction. For example, some carbon block filters can also be engineered to remove lead. NSF-International certifications are the marker to look for in these cases. (Basically, it comes down to the size of microns able to get through the filter itself).
There’s a bit of a grey area here, as any decent filter will remove some amount of most solubles. This is partly because, as described, not all activated carbon is made equal, with literally dozens of filters with different densities on the market. As a general rule, however, the removal of inorganics can only be assured by a multistage filtering process, such as reverse osmosis or distilling.
Again, Always look to NSF international certifications for the final word on what an individual filter is capable of doing.
Which filters use activated carbon?
The short answer: almost all of them. Unless it’s a heavy-duty under-sink or point-of-entry filter, nearly all models will use a carbon cartridge. Even those more industrial models will utilize carbon as one stage of their filtering process.
Pitcher filters like the Brita filter are the most well-known carbon filters, but there are other designs and options, too. Faucet-mounted filters operate in a similar way, except they use the power of the tap to pass water through the carbon, instead of relying on gravity. There are also countertop models, and most if not all types of integrated refrigerator filters use their own activated carbon cartridges.
Read: Our in-depth guide comparing the different types of water filter.
How long does a carbon filter cartridge last?
Because it’s a physical process, adsorption as a filtering principle is time-limited. Once all of the binding sites in a piece of activated carbon are used up, the filter won’t be efficient anymore. This is why all carbon filters are designed with carbon cartridges, which can be replaced periodically.
In general, activated carbon water filters can be expected to last between 2 and 6 months, depending on their size. There are a few common sense things that can affect the lifespan of a carbon cartridge—how often you filter water being the most obvious. Poorer quality water, which requires greater filtering, will also have a significant effect. In other words, the more a filter does, the shorter its lifespan.
Carbon filters are the most ubiquitous home water filtering method, and for good reason. When carbon is activated, it’s huge potential surface area and adsorptive properties are unleashed, giving water contaminants plenty of opportunities to bind to the carbon’s surface as they pass through the filter.
However, be sure to know what you’re filtering for, as the majority of carbon filters only deal with organic compounds or Volatile Organic Chemicals. That means materials such as chlorine, with a carbon base. Non-organic compounds and protozoa will mostly pass straight through a carbon filter—though, seeing as carbon filters are only intended to be used on pre-treated drinking water, you shouldn’t really need to worry about these contaminants.