Arsenic exposure in drinking water is tracked by EPA across the country; households in O Fallon, Missouri are among those with confirmed detections in the public water record.

Data: EPA SDWIS, CCR Reports, ECHO Last verified: 2026-04-05

Arsenic in O Fallon Tap Water

Arsenic has been detected in O Fallon, Missouri drinking water at a maximum level of 388 ppb — 38.8x the EPA MCL.

This analysis covers 100,311 residents across 2 ZIP codes in O Fallon.

O Fallon's overall water quality grade is C (69/100).

Is Arsenic in O Fallon Water Safe?

If you live in an affected ZIP code, consider installing a reverse osmosis filter certified under NSF 53 / NSF 58 and testing your water independently.

Arsenic Levels by ZIP Code

Average arsenic level across O Fallon: 388 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 O Fallon 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
• Missouri Water Quality
• O Fallon Water Quality
• Check Your ZIP Code