Carbon Block Vs. GAC Filters

Water sources can contain some contaminants that affect the taste of the water and other contaminants that can actually make consumers sick. Fortunately, there are water filtration products that remove many of the impurities from water. These filters often use carbon. Two dominant carbon filter choices are carbon blocks and GAC filters.

Filter Design

Granular activated carbon filters have loose granules of carbon. Solid block carbon filters have blocks of compressed carbon. Both filters are made from carbon that's ground into small particulate sizes. Carbon blocks are ground even further into a fine mesh 7 to 19 times smaller than the GAC filters.

Organic Buildup

These filters gradually accumulate organic impurities that come from the water, which serve as food for bacteria. The organics can end up back in the water. Channels also develop between the granules in the filter, leading to less effective filtration as there's less contact between the water and carbon. Carbon blocks are much tighter and won't even let through cysts. However, these filters are so fine that they can easily get plugged with matter, forcing owners to replace them. These filters can also develop bacterial contamination. Both filters need frequent cleaning for sanitation purposes.

Overall Filtration

The carbon block filters remove more contaminants than the GAC filters due to the larger surface area. The contaminants are in contact with more carbon for a longer period. Carbon blocks can remove chlorine more effectively, eliminate undesirable odors and halogenated organic compounds. The GAC carbon particles move around, so the filter does not have as much uniformity throughout, unlike the carbon blocks. The blocks have uniform pores that do not cause the water to flow through more open pores, increasing the contact time that the water has with the carbon. However, GAC filters can also filter effectively if the water has a slow flow rate that puts the water in contact with the carbon over a long time.

Filtering Radon and Benzene

GAC filters can effectively filter out radon more cheaply than aeration devices, but they can become radioactive, so operators must carefully dispose of them. These filters can also remove benzene. Radon exposure leads to increased incidence of lung cancer, and benzene has been linked to leukemia and other blood cancers.


The GAC systems are very simple and insert directly into a water purification device. Block carbon filters do not last as long as GAC filters. However, the carbon block filters are smaller than the GAC filters and can fit inside more water purification devices. Therefore, the block filters have more applications and can fit in smaller, more convenient products.