Turbidities

Turbidities, in the plural sense, describe the state or degree of turbidity—the cloudiness or haziness of a fluid caused by the presence of suspended particles such as silt, clay, organic matter, or microorganisms. Turbidity is a common property used to assess the quality of water and other liquids, and turbidities can vary with time and environmental conditions. It is a measure of how much light is scattered or absorbed by particles in the liquid, not a direct measure of dissolved substances, color, taste, or odor.

Measurement and units are standardized by nephelometric turbidity measurement. Turbidity is typically reported in nephelometric turbidity units (NTU); older forms, such as Formazin turbidity units (FTU), are conceptually similar but less commonly used today. Turbidities in natural waters are influenced by rainfall, erosion, seasonal runoff, algae activity, and sediment resuspension, while in treatment settings they reflect the efficiency of processes that remove suspended solids.

Implications of high turbidity include reduced light penetration, which can affect aquatic life and photosynthesis, increased sedimentation in reservoirs, and the potential shielding of microorganisms from disinfection. In drinking-water treatment, turbidity serves as a surrogate indicator for the effectiveness of coagulation, flocculation, sedimentation, filtration, and disinfection. High turbidity can complicate disinfection and indicate the presence of contaminants carried with particulate matter.

Removal strategies in water treatment include coagulation and flocculation to aggregate particles, sedimentation to settle them, and filtration to remove residual suspended matter. In natural and managed aquatic systems, turbidity commonly signals sediment loads and erosion risk and is monitored as part of water-quality assessment and environmental management.