Reference summary — not medical advice or a personal risk estimate.
Arsenic in drinking water
Quick answer
Classified as Group 1 — carcinogenic to humans, based on sufficient evidence in humans. Drunk. Naturally contaminated well water in some regions (parts of Bangladesh, India, Chile, parts of the US Southwest). Public water supplies in regulated jurisdictions are tested.
Summary
Arsenic, naturally present in some groundwater, is associated with cancers of the skin, lung, bladder, and others.
Detail
Inorganic arsenic and arsenic compounds are Group 1 with sufficient evidence for cancers of the skin, lung and bladder, and limited evidence for liver, kidney and prostate. Exposure is most often from naturally contaminated well water. Public water supplies are tested in regulated jurisdictions.
What's not established
This classification is based on sufficient evidence in humans that this factor can cause cancer. It does not establish a safe exposure threshold, your personal risk, or how this factor's risk compares in size to other Group 1 agents — hazard classifications are not ranked by magnitude.
Regional relevance
global
Documented in these products
Presence in a product category doesn't imply the product causes cancer. Click each to see the source and context.
Evidence sources
Every claim on this page traces back to one of these. Click through to read the primary document yourself.
Primary sources
NCI
NCI — Cancer-Causing Substances in the Environment
IARC
IARC Monographs — Classifications by Cancer Site, Vols 1–140
Supporting sources
ACS
ACS — Known and Probable Human Carcinogens
EPA
US EPA — Integrated Risk Information System (IRIS) carcinogen assessments
NTP
NTP — Report on Carcinogens (US National Toxicology Program)
Last reviewed: October 2026
Official reference list
A government list some readers use alongside the primary evidence. Meyron is not affiliated with it. A chemical being listed does not by itself describe a risk from any particular product.
- California Prop 65 list
State of California's list of chemicals known to cause cancer or reproductive harm.