A water filter on an ice maker exists for two reasons: taste and scale. Ice concentrates whatever the water carries, so chlorine, musty flavors and minerals all show up more strongly in a cube than in a glass. The filter that fixes taste and the filter that protects the machine are not always the same filter.
Why ice tastes and looks the way it does
Ice picks up flavor from two directions. The first is the water: chlorine, disinfection byproducts, sulfur notes and dissolved organics all survive freezing and are noticeable when the cube melts into a drink. The second is the freezer, since ice absorbs odors from open food and from a bin that has never been washed. Cloudiness is different again, and mostly a freezing artifact: household ice freezes fast from all sides, trapping dissolved gases and minerals in the middle as a white core. The USGS defines hardness as dissolved calcium and magnesium, classified from soft at 0 to 60 mg/L as calcium carbonate up to very hard above 180, and on harder water that mineral content makes cloudiness more pronounced and leaves scale in the machine.
Which filter for which problem
For taste, carbon is the workhorse. A carbon block cartridge on the supply line, or the fridge manufacturer's own cartridge, removes chlorine and most taste and odor compounds and is the cheapest meaningful improvement you can make. For scale in a standalone or commercial-style ice machine, a scale inhibiting cartridge that doses a small amount of polyphosphate keeps mineral from cementing onto the evaporator plate, which is the usual reason a machine slows down and starts producing misshapen cubes. For water where a test has found a dissolved contaminant, reverse osmosis at the feed point is the thorough answer, though it needs a drain connection and adequate pressure. Sediment prefiltration ahead of any of these protects the fill valve from grit.
Where the filter goes
The usual position is inline on the quarter inch supply tubing feeding the appliance, fitted somewhere you can actually reach: inside the cabinet next to the fridge, in the basement below, or at the shutoff behind the unit. Leave a service loop of tubing, mount the cartridge so it can be changed without moving the fridge, and observe the arrow for flow direction, which is a very common install error. Add a shutoff ahead of the filter. If your house already has a whole-house carbon filter, an appliance filter is a polishing stage rather than a duplicate, and if you feed the appliance from an under-sink RO system the water arrives treated and the appliance cartridge becomes a backstop only.
Changing it, and what goes wrong when you do not
Carbon cartridges do not fail loudly. They stop adsorbing, taste creeps back, and flow gradually drops as the sediment load builds. A filter left in far too long can also become a place for bacteria to grow, particularly on a line that sits unused for long periods, which is why a seasonal home should get a fresh cartridge and a good flush at the start of the season. Flush a new cartridge before trusting it, since carbon fines make the first ice gray, and discard the first batches of ice after any change. If ice stays cloudy, slow or bad tasting after a fresh filter, look at the machine: a scaled evaporator, a weak fill valve or a low supply pressure all present the same way.
Questions people ask about water filter ice maker
Will a water filter make my ice clear?
It helps but rarely fully. Household cloudiness is mostly trapped air and minerals from fast freezing, so filtering reduces it while the freezing method sets the limit.
Do I need a separate filter if my fridge already has one?
Usually not for taste. An extra inline filter is worth it where the built-in cartridge is expensive, hard to source, or where you want sediment removed ahead of it.
Why does my ice taste bad even after changing the filter?
Odor absorbed from the freezer and a dirty ice bin are common culprits. Empty and wash the bin, discard old ice, and check for uncovered food nearby.
Can hard water damage an ice maker?
Yes. Dissolved calcium and magnesium deposit as scale on the evaporator, which slows production and misshapes cubes, which is why scale inhibiting cartridges exist.