Filter Media

Activated Carbon Filter Media Granular activated carbon, a common type of filter media used in refrigerator water filters.

Filter media is the substance inside of a water filter that removes contaminants from the water supply, making it safer for ice or drinking water. The most common substance used for refrigerator water filter is activated carbon. This carbon is typically made from charcoal, though it may also be made with nutshells or wood. It’s often referred to as granular carbon or a carbon block, depending on how it’s contained within the filter.

So what makes the carbon so "active"? Well, the carbon becomes activated after it’s been processed to be extremely porous. Under a microscope, the carbon powder might look like an asteroid field, each grain covered in grooves and craters. When water passes through the activated carbon, all the tiny contaminants that may be lurking inside it are caught in these pores along the surface of each grain of the carbon. Granular activated carbon is ideal for filtering contaminants from water since each grain is larger than those found in its powdered form and thus having more pores along their surface to capture more contaminants. Carbon is also used to filter air and is sometimes used in refrigerator air filters and deodorizers.

Along with filtering water, activated carbon has an essential role in adsorption refrigeration (not to be confused with absorption refrigeration), since it acts as a kind of compressor. During the refrigeration cycle, the carbon captures the refrigerant gas as it begins to cool. When a heat source is applied, the refrigerant begins to expand, wanting to be released from the carbon. The heated gas is then directed toward the evaporator where it can expel its heat and return to the beginning of the cycle.

Activated carbon can be used in a wide variety of purification processes, one of which made famous in a recent episode of the Discovery Channel’s MythBusters television series. It's often used to filter organic vodka and whiskey of impurities before it’s processed into a product ready to hit store shelves. However, it’s been theorized that running low-end vodka through water filters that use similar activated carbon will make its smell and taste indistinguishable from high-end vodka. According to the MythBusters results site, this theory has been busted.