Turbidity, one of the important water-quality parameters, is measured in

Concept

Water-quality parameters represent different physical or chemical properties and therefore use different measurement principles.

Turbidity describes the reduction in water clarity caused mainly by suspended particles; a nephelometric instrument assesses it from the intensity of scattered light.

Application

For this item, the relevant measurement is the nephelometric light-scattering reading. That reading is reported in nephelometric turbidity units, abbreviated NTU. Therefore the measured unit is NTU.

Contrast

• Color units quantify the apparent or true colour of water caused mainly by dissolved coloured substances.

• pH units express acidity or alkalinity through a logarithmic measure related to hydrogen-ion activity.

• NTU readings arise from nephelometric measurement of light scattered by particles in a liquid sample.

• Micrograms per cubic metre express mass concentration per unit volume, commonly for material dispersed in air.

Cross-check

A turbidimeter or nephelometer reports its water-sample reading as NTU, which independently confirms the unit.

Result: NTU.