turbid

Turbid is an adjective used to describe a liquid that is cloudy or opaque due to the presence of suspended particles such as silt, clay, organic matter, or microbial cells. The word derives from Latin turbidus, meaning muddy or clouded. In scientific contexts, the related noun turbidity refers to the measure of how cloudy a liquid is.

Turbidity is commonly quantified using nephelometric turbidity units (NTU), which reflect the amount of light scattered by suspended particles rather than the amount transmitted. A turbidity measurement can be affected by particle size, shape, and color, and it provides a practical proxy for the concentration of suspended solids. Turbidity is routinely assessed in drinking water, wastewater, and environmental monitoring to gauge water quality and treatment effectiveness.

Causes of turbidity include storm runoff that erodes soil, resuspension of sediments, algal blooms, sewage or industrial discharges, and natural colloids. Particles can remain suspended for hours or days, depending on water flow, temperature, and chemistry.

Implications of turbidity vary by context. In drinking water and wastewater treatment, high turbidity can indicate contamination and can hinder disinfection by shielding pathogens from sanitizers. In ecological systems, elevated turbidity reduces light penetration, affecting photosynthesis and aquatic life. In laboratory settings, turbidity can reflect culture growth or contamination, often monitored as a proxy for cell density.

Related concepts include turbidity currents and turbidites in geology, which describe sediment movement and deposition, and turbidimetric methods used in analytical chemistry and microbiology.