A refrigerator water filter is a small activated carbon cartridge fitted into the cold water line that feeds the dispenser and the ice maker. Household pressure pushes water through a packed bed or a solid block of carbon, where chlorine, taste and odor compounds and some contaminants stick to the carbon surface before the water reaches your glass.
The path the water takes
Water enters the fridge from a small supply line behind the appliance, runs to the filter housing in the base grille or up inside the door, and is forced through the cartridge from the outside in. Carbon works by adsorption: contaminants bond to the enormous internal surface area of the media rather than being strained out by hole size. The filtered water then splits, part to the dispenser spout and part to the ice maker mold, which is why bad ice and bad water usually appear together.
What carbon holds, and what it does not
Carbon is excellent on chlorine taste, the swimming pool smell, and many organic compounds. Better cartridges add claims for lead, cysts or certain volatile organics, which appear on the box as certifications tested to a specific standard and model. What carbon does not do is remove hardness, nitrate or dissolved salts. If your ice is cloudy and your glasses spot, that is mineral in the water and no fridge cartridge will change it, because nothing in that housing removes calcium.
Why they are replaced on a schedule rather than when they fail
A carbon cartridge does not stop working suddenly. It fills up, then quietly starts passing what it used to hold, and by the time taste returns it has been doing very little for a while. Manufacturers publish a capacity and a time interval, and the shorter of the two wins. Flush a new cartridge for the volume the manual states before drinking, and if you have a bypass plug fitted instead of a filter, remember the water is going through untouched. See our replacement refrigerator water filters page for matching by model.
Questions people ask about how do refrigerator water filters work
What happens if I never change the fridge filter?
Taste and odor gradually return, flow slows as the cartridge loads with sediment, and the media can host bacterial growth on a filter left wet and exhausted for months.
Do generic refrigerator filters work as well as the brand ones?
Some do, but the fit and the certification matter. Check that the replacement lists the same tested claims for your model rather than only claiming to fit the housing.
Why is my water dispenser slow after a filter change?
Usually trapped air in the new cartridge. Run several quarts through the dispenser to purge it; if flow stays poor, the cartridge may be seated wrong or the supply line restricted.