What Does a Carbon Filter Do?

Carbon filters use a process called adsorption to remove chemicals from water. This is similar to how a sponge absorbs water, but with a much higher surface area.


A carbon filter uses granular or block carbon to purify water. Both have their own advantages and benefits, but the granular carbon filter is more effective at removing chlorine and odors.

It Removes VOCs

Carbon filters remove VOCs by a process called adsorption. This is similar to how a sponge absorbs water. When organic compounds come into contact with activated carbon, they stick to the surface like Velcro. This is because the molecules are attracted to the carbon through a chemical bonding process.

The more porous the carbon, the more it can adsorb contaminants. This is why thicker carbon filter beds are more effective than thin sheets of charcoal. In addition, the container the carbon is in also impacts its performance. If the container is too tight, it can reduce the amount of air that can pass through the filter, decreasing its dwell time and overall effectiveness.

Regulations are in place to control VOC emissions as they are known to be dangerous to health. They can cause eye, nose and throat irritation as well as headaches. Prolonged exposure can even damage the liver and central nervous system. VOCs are released into the environment by plants, animals and man-made sources such as paints, chemicals, gasoline, aerosols and wood preservatives.

The most effective way to reduce VOCs is by using a carbon filter with an appropriate CFM rating for your home. The higher the CFM, the more air is circulated and scrubbed clean of VOCs. For the best results, choose a carbon filter that is designed to work with your air conditioning system.

It Removes Chlorine

Carbon filters remove chlorine through a process called adsorption. Activated carbon has lots of tiny pores that hold onto organic compounds, including chlorine. Chlorine is a nasty contaminant that makes your water taste bad and gives off a gas you could inhale while showering. The dissolved forms of chlorine (chloramine and trihalomethane) stick to the carbon’s surface and can’t escape back into your water. This is why a large filter surface area (like those found in a pitcher) is important for better contaminant removal.

Carbon can also absorb chloramines, disinfectant byproducts, volatile organic compounds, nitrates, hydrogen sulfide, bacteria, and fluoride. This is why most whole-house carbon water filters include a prefilter for these contaminants.

Some carbon filters may be certified to remove other toxins, like coliform, cysts, lead, arsenic, and iron and heavy metals. Check for an NSF certification to see what a particular carbon filter is capable of removing.

The best carbon filters remove these contaminants and a wide range of other unwanted molecules. This includes VOCs that can be released from construction materials, paint, thinning agents, cleaning products, and cigarette smoke. These gases can cause everything from nausea and headaches to cancer and even death. A carbon filter can reduce odors from these sources and other indoor pollutants. Carbon filters can also be used for cannabis growing to reduce odors and pathogens.

It Removes Fluoride

Fluoride is a mineral that naturally occurs in some water. It’s also added to some public water supplies because it is believed to prevent tooth decay. Carbon filters can reduce the amount of fluoride in your drinking water. However, they cannot remove all of it as some is dissolved in other substances like calcium carbonate or iron oxides.

Carbon filters can, through a process called adsorption, rid your drinking water of fluoride and other unhealthy contaminants. This is because carbon has extra surface area, allowing gaseous contaminants to adhere to it in the same way that water sticks to a sponge.

The best carbon filter for fluoride removal is one that utilizes granular activated carbon. Coconut shell carbon, a popular choice, is also very good for this application because it’s made from a renewable resource. This type of carbon can even be used to rid your water of hydrogen sulfide (the “rotten egg” smell that some well water has) and it’s effective at reducing chloramines, the toxic combination of chlorine and ammonia that is sometimes used by city water treatment plants.

Carbon also works at removing many other harmful chemicals. According to the Natural Resources Defense Council, a non-profit group that doesn’t promote any particular brand of filter, carbon can rid drinking water of chlorine, disinfecting products, heavy metals (arsenic, cadmium, copper, lead, mercury and chromium), radio-nuclides, volatile organic chemicals (such as dichlorobenzene, methyl tert butyl ether and tricholoroethylene) and pesticides.

It Removes Odors

Activated carbon filters remove odors by a process called adsorption. During adsorption, molecules stick to the surface of the carbon filter and stay there. This happens because the carbon is treated to increase its surface area, which in turn increases the number of pores. The pore size is measured using the iodine and phenol tests, which also tells you how much a specific type of chemical can be adsorbed.

This is what makes carbon filters so effective at controlling odors from things like tobacco smoke, strong cooking smells and chemical fumes. These volatile organic compounds can be incredibly irritating and even toxic for the family members who live in the home, especially those with asthma, allergies or other respiratory conditions such as COPS and MCS.

The key to getting a carbon filter to work is to make sure it is placed where air can pass through it. This can be through vents, windows or exhaust systems that are designed to push or pull air through the filter. Once air passes through the carbon filter, it is scrubbed clean of odors and VOCs. If the container that a carbon filter is stored in doesn’t fit well, then bacterial growths can form on the carbon, which will reduce its effectiveness and possibly introduce bacteria into your drinking water. Regular backwashing and replacement of the carbon filter is a good way to avoid bacteria build-up.