Caffeine
Cities measured
87
Detected in
87 / 87
Highest
0.88 μg/L — Delhi
Overview
Caffeine is the world's most widely consumed psychoactive substance. It enters water via human excretion, coffee/tea processing effluent, and pharmaceutical manufacturing. Like carbamazepine, it is used as a wastewater tracer — its river concentration reliably indicates urban sewage input.
Health Relevance
At environmental concentrations (ng–low μg/L), caffeine has no known adverse health effects in humans. It causes reproductive and behavioural effects in invertebrates at μg/L concentrations.
Regulatory Limits
Drinking Water Directive 2020/2184
No EU regulatory limit.
Controversy & Contested Science
Caffeine was among the first pharmaceuticals detected in drinking water, generating significant public concern in the early 2000s. Scientists generally characterised concentrations as negligible health risks. However, caffeine's ubiquity serves as an uncomfortable reminder that wastewater treatment is not a complete pharmaceutical barrier. Cities with high coffee-shop density and large populations consistently export caffeine loads to their receiving rivers — the 'coffee signature' of urban water has been mapped across European waterways.