Activated Carbon Filters 101

An activated carbon filter has remarkable taste, odor, and chlorine reduction capabilities. Water treatment plants treat water with chlorine and chloramines that create cancer-causing by-products. These disinfectants linger in your drinking water, tainting it with a chemical flavor. Carbon clears water of organic compounds that make your water taste or smell bad. Contaminants adhere to the surface of a carbon filter, and only clean water flows to your house. 

What are carbon filters?

Carbon filters, like all water filters, are barriers that capture substances that contaminate your drinking water. Ancient Egyptians were the first to discover carbon's detoxifying powers. Carbon is still used today to remove contaminants from water, making foods and beverages taste and smell better. 

How does a carbon filter work?

Carbon filters remove contaminants through adsorption. Absorption soaks up particles like a sponge to water. Adsorption adheres particles to a surface like a piece of Velcro. Organic compounds bond or stick to the surface of a carbon filter because water and contaminants are both polar compounds that attract one another.

Carbon filters are extremely porous and have a large surface area, making them effective at reducing bad tastes, odors, and other particles in water. A carbon filter acts as a parking lot with pores for parking spaces for contaminants as water flows through. The tiny pores are measured in microns. The smaller the micron, the finer the filtration. Low flow rate and pressure give contaminants more time to park or adhere to the carbon. The more contact time water has with the surface of a carbon filter, the more efficient the filtration.  

What is a charcoal filter?

You'll often hear carbon filters referred to as charcoal filters. However, carbon filters are not made of the same type of coal used to grill burgers. 

What's inside a carbon filter?

• Bituminous coal
• Wood-based media
• Coconut shell media

Of the three types of filter media, coconut shell carbon is the most renewable. This type of carbon is made from the shell of a coconut rather than the meat inside, so it doesn't cause allergic reactions or flavor water. Wood-based carbon is made from burned wood ground into a granule and resembles what the ancient Egyptians would have used. Bituminous coal used less frequently today since traces of arsenic have been discovered in the media. 

What is activated carbon and how does it filter water?

Carbon is activated by heat or steam. The activation process opens the pores of a carbon filter, increasing the surface area and giving the carbon more capacity to hold contaminants. For this reason, all the carbon filters we supply are made from activated carbon in the form of granular activated carbon (GAC), carbon block, or radial carbon filters.

Types of carbon filters

Granular activated carbon filters

GAC filters contain loose granules of activated carbon that allow water to flow through easily. Water flows in one direction through the cartridge and contacts carbon in the process. 

Advantage: Not as restrictive. Water flows through the carbon at a faster rate. 

Disadvantage: Channeling. Water can cut a path through the carbon and allow contaminants through. 

Carbon block filters

Carbon block is made of fine granules held together with a bonding agent, which only takes up 15% of the surface area. Impure water flows in through the side of the filter and sends filtered water our through the top. As carbon is ground to a finer granule, the surface area increases. 

Advantage: Gives 7-10 times more surface area than GAC filters, and the compact carbon prevents channeling. 

Disadvantage: More flow restrictive.

Radial flow GAC carbon filters 

Radial flow carbon filters combine the surface area of the carbon block with the flow rate of the GAC filter. Water flows to the filter through the side of the cartridge radially like a carbon block but contains granules for increased flow like the GAC.

Are carbon water filters safe?

Carbon water filters are safe, especially if they've been rated by a third party for material safety. All carbon filters are rated for CTO (chlorine, taste, and odor) removal, and sub-micron carbon blocks remove other contaminants like lead or cysts. Activated carbon block filters with sub-micron ratings go above and beyond to remove additional particles through mechanical filtration. Mechanical filters work like a screen door-- they keep unwanted elements out and let clean water through. Pores of a carbon block filter that measure less than one micron are too small for cysts to pass through.

What do activated carbon filters remove?

Activated carbon filters are best at removing chlorine and bad tastes or odors, but may be certified to remove other contaminants. Look for the NSF certification on a carbon filter to find out exactly what it's capable of removing.

• Bad tastes and odors? YES
• Chlorine? YES
• Trihalomethanes (THMs)? YES
• Mercury? YES
• Pesticides and herbicides? YES
• Iron or heavy metals? If certified
• Lead? If certified
• Bacteria? If certified to remove coliform
• Hard water? NO
• Fluoride? NO
• Total dissolved solids (TDS)? NO

Dissolved minerals like calcium and magnesium sail right through a carbon filter. However, a carbon filter with a pore size smaller than one micron can remove coliform, cysts, lead, arsenic, or iron and other heavy metals through mechanical filtration. Even though these contaminants don't adhere to the carbon, they cannot fit through the small pores. 

Often materials are added to carbon to improve its reduction capabilities. Adding silver to carbon creates a media that kills bacteria. Iron-reduction carbon includes KDF (Kinetic Degradation Fluxion) media made of ground copper and zinc to create a chemical reaction. The KDF converts heavy metals from a ferrous (dissolved) to a ferric (solid) state to capture the solids in the matrix of the carbon. Although certain carbon blends can reduce coliform, a UV system disinfects bacteria-infested water most effectively.

Activated carbon and chlorine

Removing chlorine is the most common reason to use a carbon filter. Chlorine makes your food, beverages, and drinking water nasty and emits a gas that you could inhale in the shower. Chlorine does not adhere to carbon. Instead, a carbon filter removes chlorine through a chemical reaction. Activated catalytic (more reactive) carbon chemically alters the chlorine molecules, converting them into a chloride.

Many water treatment plants use this chemical to disinfect water  because it's a stable compound and does not dissipate like chlorine or create by-products like trihalomethane. However, chloramine makes water taste and smell bad. Chloramines are more difficult to remove than chlorine, so catalytic carbon is used. When chloramine hits the carbon filter, the carbon breaks the ammonia from the chlorine and turns it into chloride. 

Alternatives to carbon water filters

Carbon filter vs. sediment filter

Carbon and sediment filters serve two different functions. Sediment filters catch dirt and debris, while carbon captures organic compounds that cause bad tastes and odors. A sediment filter is a mechanical filter. It has a certain porosity that water can flow through but not anything larger than the micron rating of the filter. Because a carbon filter removes particles by adsorption, it does not make a good sediment filter. You often need one of each. 

Carbon filter vs. ceramic filter

A ceramic filter is another mechanical filter with a pore size small enough to block some living organisms. Often, carbon is either blended with ceramic or added to the inner core of a ceramic filter to enhance the scope of reduction or target specific types of contaminants. Adding carbon inside of a ceramic filter gives both carbon and sediment filtration to reduce some chemicals as well as debris. 

Learn more about how a ceramic filter works.

Carbon filter vs. reverse osmosis

Carbon filtration and reverse osmosis are two different processes that work in conjunction with one another. A reverse osmosis system separates dissolved inorganic compounds and radionuclides, unlike a simple carbon filter. Contact with chlorine can damage the RO membrane, so carbon filters are used within the system to protect the membrane. Carbon filtration is part of a reverse osmosis system incorporated at different stages of the filtration process. 

Learn more about how reverse osmosis filters water, the stages of reverse osmosis, or how to select the best RO system. 

When and where should you use a carbon filter?

You can use a carbon filter in several places. It can be used for point-of-entry (POE) to filter the whole house or point-of-use (POU) to clean water before you drink or cook with it. Some shower heads include carbon filtration to prevent you from inhaling chlorine gas in the shower. Carbon filters are also part of a reverse osmosis system or an ultrafiltration (UF) system. A carbon filter added to a UF system provides organic and chemical particulate reduction along with lead reduction.  

If you use a water softener to soften water treated by a municipal plant, then you should install a carbon filter before the water softener. If chlorine is removed prior to softening, then the softener resin lasts longer. Chloramines can cause O-rings, gaskets, and rubber seals to deteriorate, so removing chemical disinfectants with catalytic carbon helps water-using appliances, like your tankless water heater, last longer. 

Learn more about an ultrafiltration membrane or how a water softener works.

How often should you change your carbon filter?

Change your carbon filter every six months to one year. Never use a carbon filter for longer than one year. Waiting to change the filter could make your water worse than it was before treating it. If the pores of a carbon filter are full, collected particles will begin to break from the carbon and flow into your water supply. 

Is a carbon filter effective?

Carbon filters are excellent at removing chlorine and other disinfection by-products like trihalomethanes and bad tastes and odors. Some are rated to reduce other contaminants by filtering them mechanically. However, if your water contains high levels of inorganic compounds and dissolved solids, use a reverse osmosis system to treat it. 

Carbon Filtration Pros and Cons

Pros

• Effective taste, odor, and chlorine reduction
• Lots of surface area
• Reduced health hazards
• Protection for other filtration systems or softeners

Cons

• Does not remove dissolved solids and other inorganic compounds
• Frequent filter changes required