What Do Refrigerator Water Filters Actually Remove?
There is a good chance your San Marcos kitchen already has a filter in the refrigerator door, and an equally good chance you have assumed it handles whatever needs handling. It does do a real job. It just does a narrower one than most people think.
The short version: a fridge filter is a carbon filter. Carbon is good at chlorine, taste and odor. It is not designed for dissolved contaminants like nitrate, fluoride, arsenic or PFAS — and those are the ones that show up in the San Marcos water quality report.
What a Refrigerator Filter Does Remove
Most refrigerator filters are activated carbon, and most are NSF certified to reduce chlorine taste and odor, sediment, and to some degree lead, asbestos and pharmaceuticals. That is genuinely useful — chlorine is what makes tap water taste like a swimming pool, and San Marcos water carries around 1.35 ppm of it.
Two caveats matter. Carbon filtration depends on contact time, so performance drops as flow rate rises. And the filter only works while it has capacity left. An overused cartridge does not simply stop working — water can push past the trapped contaminants and carry them through. Because the filter is out of sight inside the door, this is the single most common failure: people forget, and a filter that should be changed every six months runs for two years.
What It Does Not Remove — And Why That Matters Here
Carbon does not remove dissolved solids. That puts arsenic, fluoride, nitrate and radium outside what a fridge filter can do, whatever the packaging implies.
It also matters locally. The San Marcos water quality report shows total trihalomethanes around 65 ppb and haloacetic acids around 19 ppb — both disinfection byproducts formed when chlorine reacts with organic matter — plus four detected PFAS compounds and nitrate around 2 ppm. All of it is within federal limits, and none of it is what a carbon fridge filter was built to address.
| Contaminant | Fridge carbon filter | Under-sink reverse osmosis |
|---|---|---|
| Chlorine taste and odor | Yes | Yes |
| Sediment | Yes | Yes |
| Lead | Partially, if certified | Yes |
| Disinfection byproducts (TTHMs, HAA5) | Limited | Yes |
| Nitrate | No | Yes |
| Fluoride | No | Yes |
| Arsenic | No | Yes |
| PFAS | No | Yes |
A Culligan reverse osmosis system pushes water through a semi-permeable membrane, which is what allows it to take out dissolved contaminants a carbon filter passes straight through.
The Dispenser Is Its Own Problem
One of the bigger issues with fridge filtration is not the filter at all. The National Sanitation Foundation found the water dispenser to be among the germiest spots in the kitchen, with most carrying yeast or mold, and the same applies to the ice dispenser. For anyone with allergies or a compromised immune system, that is worth knowing — and it is a cleaning problem, not a filtration one.
Is Your Fridge Filter Good Enough?
If all you want is water that tastes better than it does from the tap, and you are disciplined about changing the cartridge, a fridge filter is fine. If what is prompting the question is the contaminant list in the annual report, it is not the right tool — and neither is a pitcher filter, which is the same carbon technology in a different shape.
An under-sink reverse osmosis system covers both jobs with less maintenance and no cartridge to forget. Culligan of San Marcos serves San Marcos, Buda, Kyle, Dripping Springs, Wimberley, Woodcreek, Driftwood, Blanco, Johnson City and Lockhart.
