Arsenic water filters divide cleanly into two families that work and several popular products that do not. Reverse osmosis and adsorptive media, meaning iron oxide or activated alumina beds, remove arsenic. Standard carbon blocks, softeners and sediment cartridges do not. The complication is that arsenic exists in two forms in groundwater and only one of them is easy to remove, so the test result decides the equipment.
Arsenite and arsenate are not the same problem
Arsenic occurs naturally in bedrock across large parts of the country and dissolves into groundwater without any human source. In oxygen-rich water it exists mostly as arsenate, which carries a charge and is readily caught by adsorptive media and rejected by a membrane. In oxygen-poor deep wells it exists as arsenite, which is uncharged and passes straight through equipment that handles arsenate well. That is why a system that performed well on a neighbor's well can fail on yours. The standard fix is pre-oxidation, usually a chlorine or similar oxidant stage that converts arsenite to arsenate before the removal stage, so the filter sees the form it can hold.
Point-of-use reverse osmosis
For drinking and cooking, an under-sink reverse osmosis unit is the most common answer. The membrane rejects arsenate strongly, the equipment is well understood, and the treated water is stored in a small tank so the low production rate does not matter. Its limits are the same as always: it sends reject water to drain, it needs adequate line pressure, and the membrane must be preceded by carbon so chlorine does not damage it. Because arsenic is ingested rather than absorbed through skin during normal household use, treating just the drinking tap is a legitimate strategy rather than a compromise, and it is far less equipment than treating the entire supply.
Whole-house adsorptive media
Where you want every tap treated, or where the arsenic level makes point-of-use feel too fragile, the whole-house route is a tank of adsorptive media, typically an iron-based granular medium or activated alumina, plumbed at the point of entry. These beds hold arsenic until the capacity is used up, at which point performance falls off rather than the unit failing visibly, which is why scheduled sampling of the treated water is part of owning one. Competing ions matter: silica, phosphate and high pH all shorten media life. Iron in the raw water can help, since arsenic co-precipitates with iron, and an existing iron filter often removes some arsenic incidentally.
Test before you buy, and test again after
Nothing about arsenic is visible, tasteable or smellable, so the only way to know is a lab test. This matters most for well owners: the EPA notes that private wells are not federally regulated under the Safe Drinking Water Act, that around 15 percent of the US population relies on them, and that a USGS study of 2,100 private wells found about one in five carried at least one contaminant above a human-health benchmark. Ask the lab for total arsenic and, if the level is a concern, for speciation so you know whether you need a pre-oxidation stage. Our well water testing guide covers how to collect a sample the lab will accept.
Questions people ask about arsenic water filters
Does a carbon filter remove arsenic?
No. Standard activated carbon is not an arsenic removal technology, and a pitcher or fridge filter should not be relied on for it.
Does boiling water remove arsenic?
Boiling makes it worse. Water evaporates and the arsenic stays behind, so the concentration in what is left rises.
Will a water softener take arsenic out?
No. Ion exchange softening targets calcium and magnesium and is not designed or rated for arsenic removal.
Do I need to treat the shower water too?
Arsenic is a concern through ingestion rather than skin contact, so treating drinking and cooking water is the usual approach.