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Why do drinking-water standards include limits for turbidity?

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Diagram of a water treatment plant showing the process from water inlet through mixing, coagulation, flocculation, settling, filtering, chemical treatment with chlorine, storage, and high-lift pumping to the distribution system. — water purification Water from inlets located in the water supply, such as a lake, is sent to be mixed, coagulated, and flocculated and is then sent to the waterworks for purification by filtering and chemical treatment. After being treated, the water is pumped into water mains for storage or distribution.

Drinking-water standards include limits for turbidity primarily because it poses a significant risk to public health by interfering with the disinfection process.12

Turbidity refers to the cloudiness of water caused by suspended particles such as silt and clay. These particles can create a physical shield for pathogenic organisms, protecting them from the chemicals used to treat the water. Because this interference undermines the effectiveness of water treatment, turbidity is classified under primary drinking-water standards, which are specifically designed to protect public health.132

Beyond these health implications, turbidity is also generally considered objectionable to consumers due to its appearance. While groundwater typically has very low turbidity due to natural filtration through soil, surface waters often require treatment to meet these safety standards.1