Carbon filtration is used where taste or odour of a water supply is an issue and can be either a carbon block, or in the form of granular activated carbon. GAC consists of charcoal that has been heated to a very high temperature. Each granule is porous and has a very large surface area (500m2 per gram). As water passes through the charcoal, the granules trap the molecules of pollutants and chemicals that taint the water such as chlorine and volatile organic compounds.
Carbon is extremely effective at improving taste, and reducing any smell in water. A GAC or carbon block can be added to a pre UV filter and is worth considering if the water is likely to be consumed.
It is recommended that carbon filters should be changed once a year or more frequently where there is any hint of change in smell or taste. Carbon filters do not kill bacteria so are part of the pre treatment process.