In Caldwell, Idaho, Arsenic has been detected in the public water supply — a contaminant that health agencies track because of documented effects associated with prolonged exposure at elevated concentrations.

Data: EPA SDWIS, CCR Reports, ECHO Last verified: 2026-05-14

Arsenic in Caldwell Tap Water

Arsenic has been detected in Caldwell, Idaho drinking water at a maximum level of 12 ppb — 1.2x the EPA MCL.

This analysis covers 75,858 residents across 3 ZIP codes in Caldwell.

Caldwell's overall water quality grade is C (64/100).

Is Arsenic in Caldwell Water Safe?

Arsenic was detected in Caldwell water but currently falls within EPA limits. However, some health organizations argue the EPA MCL may not be protective enough.

If you are concerned, a reverse osmosis filter can reduce arsenic levels further.

Arsenic Levels by ZIP Code

Average arsenic level across Caldwell: 12 ppb

Health Effects of Arsenic

• Increased risk of skin, bladder, lung, and kidney cancer
• Cardiovascular disease and type 2 diabetes
• Skin changes (darkening, thickening, lesions)
• Developmental effects in children exposed in utero

Health risk severity: High. Governed by the Arsenic Rule (2006).

How Arsenic Gets Into Drinking Water

• Natural deposits in rock and soil (especially in western U.S.)
• Runoff from orchards and glass/electronics production
• Historical use of arsenic-based pesticides
• Well water in areas with arsenic-rich geology

What to Do About Arsenic in Caldwell Water

1. Install a reverse osmosis (RO) system certified under NSF 58
2. Adsorptive media filters (iron-based) can also reduce arsenic
3. Have well water tested if on a private supply
4. Boiling water does NOT remove arsenic — it concentrates it

Look for filters certified under NSF 53 / NSF 58 for arsenic removal.

Related

• Arsenic — National Overview
• Idaho Water Quality
• Caldwell Water Quality
• Check Your ZIP Code