Turbidity
Cities measured
87
Detected in
87 / 87
EU limit
4 NTU
Highest
1.9 NTU — Karachi
Overview
Turbidity measures the cloudiness of water caused by suspended particles — clay, silt, algae, and organic matter. It is expressed in Nephelometric Turbidity Units (NTU). Low turbidity is a prerequisite for effective UV and chlorine disinfection; particles can shield pathogens from treatment.
Health Relevance
High turbidity can protect pathogens from disinfection. WHO recommends < 1 NTU to ensure effective treatment. Turbidity spikes in source water often precede waterborne disease outbreaks.
Regulatory Limits
Drinking Water Directive 2020/2184
< 1 NTU (recommended for disinfection efficacy)
Controversy & Contested Science
The 1993 Milwaukee Cryptosporidium outbreak — the largest documented waterborne disease outbreak in US history, infecting 403,000 — was preceded by turbidity spikes that went unreported. Post-outbreak analysis showed the utility had been averaging turbidity data across monitoring points, masking localised exceedances — a practice the EPA subsequently prohibited. Critics argue turbidity averaging remains common practice globally and that point-of-treatment monitoring is inadequate.