A long-unexplained signal in chloraminated drinking water has been identified as chloronitramide anion (Cl–N–NO₂⁻), a product of inorganic chloramine decomposition. Researchers found it in all 40 samples they tested from 10 U.S. water systems. The finding establishes its presence in those samples—not that it causes harm or that tap water is unsafe.
What was identified—and what “first detected” means
The newly identified compound is chloronitramide anion, written Cl–N–NO₂⁻. In a 2025 study, Fairey and colleagues reported it as a previously unidentified end product of inorganic chloramine decomposition. The chemical structure was not known when the signal was first observed.
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More than 40 years ago, water researchers noticed an unexplained interference in ultraviolet-absorbance monitoring of monochloramine and dichloramine. That observation concerned a signal in the measurement, not a confirmed identification of chloronitramide. The 2025 work connected the longstanding signal to the anion’s chemical identity.
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What the water samples showed
The researchers detected chloronitramide anion in all 40 samples collected from 10 chloraminated U.S. drinking-water systems. Concentrations varied substantially among the samples:
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- Median: 23 micrograms per liter
- First quartile: 1.3 micrograms per liter
- Third quartile: 92 micrograms per liter
- Maximum: 120 micrograms per liter
These figures describe the study’s samples. They are not a national estimate, and the results do not establish how concentrations vary across locations or over time.
Why chloramines are used in drinking water
Inorganic chloramines are used as disinfectants in drinking-water treatment. The study describes their purpose as protecting public health while helping curb the formation of regulated disinfection by-products. The identification of a decomposition product adds to the chemistry that researchers need to understand; it does not show that chloramine disinfection is ineffective or that systems should change treatment.
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The broader context is that roughly 1,000 drinking-water disinfection by-products had been identified since 1974, according to a 2026 review by Jiafu Li and Susan D. Richardson in TrAC Trends in Analytical Chemistry. That count covers disinfection by-products broadly, not chloramine by-products alone.
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Does its detection mean it is dangerous?
No health-effect conclusion is established by the reported detection. Finding a chemical in water confirms its presence in the tested samples; by itself, it does not show that exposure harms people, establish a safe or unsafe dose, or determine the risk at the measured concentrations. Concentration alone also cannot be used to compare its danger with regulated contaminants.
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The study calls for further occurrence and toxicity studies. Its authors note that chloronitramide warrants investigation in chloraminated systems serving more than 113 million people in the United States. That figure describes the population served by such systems, not the number of people shown to have been exposed to a harmful dose.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What remains to be learned
- How commonly chloronitramide occurs beyond the 10 systems and 40 samples studied.
- How its levels change over time and across water systems.
- Whether exposure at relevant levels has health effects.
The study does not establish whether household filters or other consumer treatments remove the compound. It also does not validate a consumer test for measuring it. Until occurrence and toxicity are better characterized, the discovery is a reason for further scientific study—not proof of a health threat.
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