Arsenic in well water

Naturally occurring. Tasteless, odorless, colorless. Arsenic is the clearest reason a well needs a test instead of a taste check.

Where it comes from

Arsenic in groundwater is almost always geological, leached out of certain bedrock and sediment types, not pollution. USGS research maps it as more concentrated in parts of New England, the upper Midwest, and parts of the Southwest, but local variation inside those regions runs high. A well can sit well above or below a neighboring well's reading depending on the specific aquifer it draws from.

The EPA level

The Maximum Contaminant Level is 10 µg/L (micrograms per liter), based on long-term cancer and non-cancer risk from chronic exposure. There's no acute symptom to notice, which makes "the water tastes fine" an unreliable assumption for this one specifically.

What to do about a high reading

Reverse osmosis and adsorptive media, activated alumina or iron-based media, are the standard treatment approaches. A whole-house system differs from a single tap. Arsenic can vary by season and by how a well is pumped, so a second confirmatory sample from a state-certified lab is worth doing before installing anything.

Have a lab result already? Upload it and check your arsenic reading.