Carbon readily absorbs organics and chlorine, and is therefore used to filter such elements from feedwater. Chlorine must be removed from feedwater for use in reverse osmosis and all distillation systems because chlorine will attack membranes and stainless steel. Chlorine can cause stainless steel to stress crack corrode due to the elevated temperatures at which distillation systems operate.

Various grades of carbon, including regular carbon, medical grade and coconut shell help to break down chloramines, a compound comprising chlorine and ammonia. These and other grades of carbon can be added to the filter for specific pre-treatment needs. The filters need to be designed for steam sterilization or hot water sanitization to kill the bacteria that can grow in carbon filters. Typically this is done on a weekly basis.

Carbon filters are usually backwashed twice a week to make sure the carbon does not compact and allow feedwater to channel through the carbon filters. To meet these needs, the carbon filters are designed with stainless steel vessels and piping to handle the hot conditions caused by steam or hot water.

Many municipalities today use carbon as a biocide replacement for chlorine. Because carbon filters remove chlorine from the feedwater, bacteria growth and control must be addressed in the design of carbon filters.

To ensure the breakdown of chloramines, carbon beds should be sized for less than one gallon per minute of feedwater flow per cubic foot of carbon. In this process, the carbon effectively removes the chlorine portion of the chloramine, leaving the ammonium ion in the feedwater. Ammonium ions can be removed through water softening.