In most refrigerators with a dispenser or an ice maker, yes, the water passes through a filter cartridge on its way in. That filter is a small carbon block, and what it does well is taste and odor. What it does not do is everything people assume a filter does, and an expired cartridge quietly does nothing at all.
What is inside the cartridge
The typical refrigerator filter is a compact carbon block in a plastic shell with a bypass valve, sized to fit a specific model. Carbon adsorbs chlorine, the compounds that carry musty or chemical tastes, and some organic chemicals. Better cartridges carry certifications for additional reductions, commonly lead and cysts. The certification listed on the box, not the price, is what tells you the range of the filter you are buying.
What it does not remove
Dissolved minerals pass straight through, so water from a fridge dispenser in a hard water house is exactly as hard as the water at the kitchen tap and will still leave cloudy ice and scale in the ice maker. Nitrate passes through. Bacteria are not removed and the cartridge is not a disinfection device, which matters on an untested private well. If you need those things addressed, the fridge filter is not the machine to do it.
Not every fridge filters, and not every filter is working
Some models have no filter at all, and many have a bypass plug fitted where a cartridge should go, most often after a service or a house move. Check your model and look for the cartridge housing, in the upper right of the fridge compartment, behind the grille at the base or in an external inline housing behind the appliance. Manufacturers publish which cartridge fits which model and what it is certified to reduce.
Changing it, and knowing your supply
Carbon exhausts by volume, not by taste, so the six month interval most manufacturers publish is a floor rather than advice to ignore. Once exhausted the cartridge is a warm plastic cylinder of wet carbon in the water line, and it can make water taste worse than no filter at all. Every community water system publishes an annual Consumer Confidence Report and the EPA maintains a finder for it, so read yours: it tells you whether a carbon cartridge covers what your supply actually carries or whether you need a proper under-sink system.
Questions people ask about is fridge water filtered
How often should a fridge water filter be changed?
About every six months for most models, or sooner if flow drops or the taste changes. The interval is based on volume filtered, not on the water looking fine.
Can I run my fridge without a water filter?
Usually yes, with the bypass plug that came with the appliance. The water is then unfiltered, which is fine on a supply you already treat elsewhere.
Does a fridge filter soften water or remove hardness?
No. Carbon does not remove dissolved calcium and magnesium, so ice and dispensed water stay exactly as hard as the incoming supply.