Granular Activated Carbon (GAC) vs. Activated Carbon Block (CB) Water Filters

Granular Activated Carbon (GAC) vs. Activated Carbon Block (CB) Water Filters

Activated carbon filters are typically used as a complimentary filter to a pre-filter that removes the sediment, carbon filters are designed to remove undesirable tastes, odors, and are very effective in removing free chlorine from water from a potable water source. They are also commonly used as finishing filters for Ultra-Violet (UV) and Reverse Osmosis (RO) water filtration systems. When selecting an activated carbon filter for these types of systems, you have two options: Granular Activated Carbon (GAC) or Carbon Block (CB). Both GAC and CB filters are manufactured using an activated carbon media, however this is where the similarities end.


Carbon filters remove contaminates by absorption, the greater the surface area, the more contact the water has with the carbon media, and the length of time for which the water is in contact both with the carbon both increase the effectiveness of the filter. Carbon block filters have a much larger surface area, which allows them to filter larger volumes of water while also being much more affective at filtering out taste and odors, particles, heavy metals, and other contaminants. This does not mean that granular activated carbon filters are necessarily a bad choice. What is important is that you understand the differences and the trade offs between these two types of filters so you can make an educated decision. The information below provided the advantages and disadvantages for both granular activated carbon and carbon block filters.


Before using carbon filters as standalone filter, one must confirm that the water supply is “potable” or “safe for human consumption,” the water must be tested by a qualified water specialist to confirm the water is microbiologically safe. If the water supply is un-safe a water treatment / purification system, such as an RO or UV filtration system to remove harmful contaminants present in the supply water will be required. The CB or GAC carbon filters are installed as secondary or finishing filters with these water treatment systems to remove  undesirable odors and improve the taste of “safe” drinking water.

Granular Activated Carbon (GAC)

Granular activated carbon filters are manufactured using carbon that has been ground to a coarse granular structure which is contained loosely inside a cannister type cartridge. The loose nature of granular carbon in GAC filters means that they can provide a much higher flowrate than CB filters, which means that you can filter more water in less time. The trade off is that GAC filters are less effective than CB filters. However, the effectiveness of GAC filters can be increased by slowing down the flowrate using a flow control, increasing the amount of time that the water is in contact with the carbon to allow absorption of the contaminates. Granular activated carbon filters do have the advantage of lasting much longer than carbon block, although they do not provide the same level of contaminate removal as carbon block filters as they are more prone to the following issues.

Channeling – Is a common issue with GAC filters, in the loose carbon bed of granular carbon as water travels through the filter finding the path of least resistance. When channeling occurs water bypasses carbon in the filter thereby the adsorption capacity of carbon is under-utilized.

Microbiological Growth / Dumping - In a loose bed of carbon, stationary pockets of water can develop due to changes in water pressure and flow rates, these pockets of can result in bacterial growth, when these pockets collapse, "dumping" of the contaminated water into the water system can occur.