In the U.S., more than 90% of community water supplies are treated with chlorine to kill harmful organisms. While this makes water safe from germs, it also produces chemical byproducts called trihalomethanes (THMs). And these chemicals cause chronic kidney disease (CKD), according to a new study in JAMA Network Open.
Researchers used data from the California Teachers Study, tracking 89,320 women from the mid-1990s through 2018. They calculated each woman’s long-term exposure to four types of THMs using annual water measurements from 1995–2005, also factoring in other toxins like uranium and arsenic.
Findings:
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● 6,242 participants developed CKD during follow-up
● Average total THM: 5.5 µg/L (top 5%: ~58 µg/L)
● Average brominated THM: 2.7 µg/L (top 5%: 30 µg/L)
● Brominated THM ≥30 µg/L → 43% higher CKD risk
● Even moderate exposure (75th percentile) → 23% higher CKD risk
● Brominated THMs contributed 53% of total CKD risk, followed by uranium (35%), arsenic (6%), and chloroform (5%)
Crucially, these risks appeared below the current U.S. safety limit for total THMs (80 µg/L).
Protect yourself:
Check your local water utility’s annual quality report for chlorine and THM levels. If they’re high, consider a carbon-based filter, like many pitcher or under-sink systems, and replace filters regularly.