Turbidity can be interpreted as a measure of the relative clarity of water. Turbidity is not a direct measure of suspended particles in water but, instead, a measure of the scattering effect such particles have on light. See more about the science of turbidity
Today, many methods exist for the determination of water contaminants, yet turbidity measurement is still important because it is a simple and undeniable indicator of water quality change. A sudden change in turbidity may indicate an additional pollution source (biological, organic or inorganic) or may signal a problem in the water treatment process.
In practical applications significant problems can introduce interference and errors that reduce the accuracy of any instrument. To ensure the instrument is operating properly and providing the most accurate answers possible, it is important to verify its calibration. See more about standards and calibration