Granular vs Block Carbon Water Filters
Carbon Filtration
Carbon based filters are essential for removing organic compounds including those that are volatile, such as components of gasoline, solvents and industrial cleaners, trihalomethanes (THMs), pesticides, herbicides, and chlorine. They are also used for taste and odour improvement. What carbon filters don’t remove are mineral salts, dissolved solids, heavy metals or fluorides. 

Carbon filters remove contaminants through adsorption. Adsorption is a process where contaminants are attracted to the surface of the activated carbon and are held there. Carbon filters are extremely porous and have a large surface area, which makes them effective at reducing bad tastes, odors, and other particles in 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. Block and granular activated carbon filters are made from carbon ground into small particulate sizes, but the major difference between the two lies in their adsorbing efficiency. Granular activated carbon (GAC) filters contain loose granules of carbon, while carbon block activated carbon filters have 
solid blocks of compressed carbon. 

Common Sources of Carbon for Water Filters

bituminous coal
coconut shells 

** Coconut shells are the most common.
** Coconut shells are highly renewable.

Carbon Block
Thanks to their larger surface area, carbon block filters have a better contaminant removal capacity than GAC filters. A major advantage of carbon block filters is that they allow for water to be in contact with carbon for a longer period, which leads to a better rate of contaminant removal. Catalytic carbon filters are a type of carbon block filter that contain a special catalytic carbon block, and are highly effective at chlorine and chloramine reduction.

CarbonGranular Activated
GAC filters lack the uniformity of carbon block filters and, given that there is less contact time of water with the GAC particles, their efficiency falls behind that of solid block carbon filters. They are often used in a polishing application in the water filtration process.

Flow Rate Considerations
Higher flow rates can be achieved with a GAC carbon filter compared to a solid carbon block filter. Block carbon filters don’t run the risk of “channelling” and are manufactured with different micron ratings. A lower micron rating can decrease the water flow. Be sure to know the micron rating when using block carbon filters as this ensures that you have the correct flow rate for the application. 
CarbonWater Filter Channelling
This occurs when water does not flow through a filter evenly. Loose filter material can open up a “channel”,  which allows the water to flow through without making contact with all of the filter's media. The process of channelling will reduce the efficiency of the filter due to the contact time between the contaminants and carbon being reduced. 

Sediment Removal
Excessive sediment in the water can reduce the ability for carbon filters to allow water to pass and will block flow entirely when sediment levels are excessive. When sediment is present in a water, ensure that it is removed properly before using a carbon filter to allow for proper filtration.

Note for Usage
Both types of filters can be a breeding ground for bacteria, which is why they need to be replaced frequently. This is especially important when they become too saturated with contaminants. Bacteria are known to replicate on the surface of carbon media. Therefore carbon filters should not be used when water is microbiologically unsafe without proper pre-treatment.


Selecting the correct carbon filter is important when treating a specific water source. This can vary depending on whether your water source is municipal, from a well or from surface water. If you are unsure, consult a water treatment professional who can assist you in making the correct choice to ensure your water safety.

Volume 5 - Issue 8 Wahl H2O - Water Awareness
Copyright 2021 Jeff Wahl – Wahl Water | All Rights Reserved
Contact Jeff via email [email protected]

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