It is a measure of the resistance offered by the particles present in water to the passage of light through water.
● Turbidity is opaqueness in water. It is caused by suspended and colloidal particles. ●The smaller the size of the particle higher is the turbidity. ● Turbidity is measured on a silica scale and expressed in terms of Turbid Units (TU) Nephelometer● Water containing 1 milligram of finely divided silica per liter has a turbidity of 1 NTU. ●It is based on color matching technique. ● The NTU is measured with an electronic instrument called a nephelometer. ● The water to be measured is placed in a standard container. A light beam passes through the water and strikes a sensor on the other side of the container. A second sensor is mounted at right angles to the beam, measuring light scattered by particles in the water. From the ratio between the light intensities at the two sensors the turbidity in NTU can be calculated. Baylis Turbidometer ● This turbidimeter is based on color-matching techniques. ● Light intensity is measured in the direction of incident light. ● Formazin is a chemical compound that produces more reproducible standards than and has been replaced as a reference. The turbidity unit is also sometimes called FTU.