What is a Carbon Water Filter?

Brad Cole

A carbon water filter can be any type of water purification system that uses carbon to remove impurities. Common examples include large municipal granular activated carbon (GAC) systems, “charcoalaquarium filters, and domestic use or countertop water filters, sometimes called point-of-use or domestic drinking water filters. Carbon water filters generally use either granular activated carbon or carbon blocks for purification, both of which remove impurities through a process called adsorption.

A glass of filtered water.
A glass of filtered water.

In a granular activated carbon water filter (GAC), water moves through small bits of activated carbon. The consistency of this carbon has been described as either fine black sand or extremely fine coffee grounds, and presents a large surface area for water to travel over. Impurities are trapped on the carbon through adsorption, resulting in cleaner water. GAC water filters can sometimes suffer from channeling, where water travels through a specific path that gives little resistance and results in little purification, if overused or improperly packed.

Carbon water filters are sometimes built into a pitcher.
Carbon water filters are sometimes built into a pitcher.

In carbon block filtration, the carbon is pressed into a single block, usually cylindrical in shape. Water is then forced through the block, resulting in purification. While carbon block filters still use adsorption to clean water, dense carbon block filters can even physically block some microbiological agents from passing through them – something that less dense filters like GACs generally can not accomplish.

A carbon water filter removes numerous impurities from water. Chlorine, volatile organic compounds (VOCs), pesticides, herbicides, and mercury are what these filters work best on. Some carbon block filters have also been designed to remove PCBs (Polychlorinated biphenyls), lead, and asbestos. Silver is sometimes added to granular activated carbon filters to provide antimicrobial properties. Carbon water filters are generally ineffective at removing other inorganic compounds, radionuclides, and many microbiological agents.

For a carbon water filter to be effective, the activated carbon must be changed on a regular basis. While there are industrial ways to “reclaim” the activated carbon, domestic users will need to replace the activated carbon during the recommended interval--usually after a specific number of gallons have been purified. Most retail carbon water filters use pre-packaged cartridges to make replacing the carbon easier, but some granular activated carbon filters can still be found that allow consumers to directly handle the carbon.

As previously mentioned, a carbon water filter uses a process called adsorption to purify water. In adsorption, small particles are removed from water or air and adhere to the surface of another substance. Carbon’s porous nature presents a large surface area that allows this process to work extremely well.

Carbon filters remove impurities via absorption.
Carbon filters remove impurities via absorption.

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