Turbidity is an optical characteristic that refers to the degree of clarity of a liquid. Turbidity in water is caused by individual suspended particles or colloidal matter that scatters or obstructs light transmittance: the higher the concentration of suspended particles/colloidal matter, the higher the turbidity. Such particles are normally too small to be detected by the human eye; therefore, turbidity measurement has to be done with a turbidity meter or turbidity analyzer. The best way to control processes that require close turbidity monitoring is with an in-line turbidity meter. An in-line turbidity meter provides a continuous measurement of turbidity that can be used for process control purposes. Everyday examples of turbid liquids are:

• Milk – contains emulsified protein/oil drops in water
• Wastewater – contains suspended particles
• Wheat beer – contains yeast cells