Due to the filtration and adsorption properties of activated carbon, many water filters today use it as an important filtration material.

Activated carbon is commonly made from materials such as coconut shells, wood, or coal. Through processes such as heating and activation, a highly porous structure is created, greatly increasing its surface area. The total internal surface area of activated carbon can be extremely large relative to its physical size, which allows it to adsorb a wide range of contaminants.

Activated carbon can adsorb many organic compounds and reduce odors and unpleasant tastes caused by certain contaminants. When specially designed and treated, it can also reduce certain chemicals and contaminants, including some pesticides, solvents, and chlorine byproducts. Its effectiveness depends on the type of carbon, the design of the filter, the contaminant, and the amount of water treated. To ensure activated carbon performs effectively, the filter media must be replaced regularly according to the manufacturer’s recommendations. Once the media becomes saturated, its ability to remove contaminants can decrease.

Activated carbon filters can also remove some suspended particles, depending on the filter’s design and pore size. However, ordinary activated carbon should not be assumed to remove very small microorganisms such as E. coli or other bacteria unless the filter has been specifically designed and certified for that purpose. Filtration of particles and microorganisms depends on the overall filter design and is not determined by activated carbon alone.

Activated carbon does not effectively remove many dissolved inorganic contaminants, such as calcium, magnesium, fluoride, nitrate, and most heavy metals. Depending on the specific contaminant, these substances may require other treatment methods, such as ion-exchange water softeners, distillation, or reverse osmosis. No single filtration method removes every type of contaminant, so the appropriate treatment depends on the quality of the source water and the specific substances that need to be removed.

By Michael Chiu, MWS, CI
Previously published in Ming Pao Daily News – Updated and Revised in 2026