Nitrite
Cities measured
87
Detected in
86 / 87
EU limit
0.5 mg/L
Highest
0.12 mg/L — Karachi
Overview
Nitrite is a transient nitrogen-cycle intermediate. In distribution systems using chloramine disinfection, bacteria can convert ammonia (released by chloramine) to nitrite — a process called nitrification. The tap-point limit is specifically set to capture this in-pipe conversion.
Health Relevance
Nitrite is more acutely toxic than nitrate, binding haemoglobin to form methemoglobin and reducing oxygen transport. The EU tap limit (0.5 mg/L) is specifically protective for infants.
Regulatory Limits
Drinking Water Directive 2020/2184
0.5 mg/L at tap (0.1 mg/L leaving treatment works).
Controversy & Contested Science
Chloramine-based disinfection systems — common in the US and some EU utilities — are vulnerable to nitrification events where pipe bacteria convert ammonia into nitrite, temporarily spiking levels in specific network zones. A 2020 US EPA study found nitrification events affecting ~40% of chloraminating utilities, often without operator awareness. The use of chloramine — a trade-off that reduces carcinogenic trihalomethane formation but enables nitrification — exemplifies the multi-layered compromise inherent in drinking water disinfection.