Turbidity:

The turbidity is an indication of the clarity of water and is defined as the optical property that causes light to be scattered and absorbed rather than transmitted in straight lines through a sample of water. Although turbidity is caused due to suspended solids the turbidity cannot be fully correlated with the quantitative measurement. It depends on shape, size and refractive indices of the suspended particles as well. The turbidity is measured by a turbidity rod or by a turbidity-meter with optical observations and is expressed as the amount of suspended matter in mg/l or ppm. The standard unit is that which is produced by 1 milligram of finely divided silica in 1 litre of distilled water. Turbidity units are expressed as NTU or JTU depending on instruments used for its measurement.