Turbidity Measurement Turbidity is used a lot when talking about water quality and the performance of water treatment plants (WTP). But what is turbidity and what do the results mean? Simply put turbidity is the amount of light scattered by water. Light passing through water is scattered by suspended and colloidal matter. Turbidity measurements are made using electronic nephelometers, which report results as nephelometric turbidity units (NTU). These instruments use light d