Turbidity, measured as NTU or FNU

Overview

Turbidity is a water-quality term that refers to the cloudy appearance of water and is caused by small particles of suspended matter. Turbidity is measured by quantifying the amount of light scattered by particles in the water. Although turbid water is not necessarily harmful, it can be an indicator of more serious problems. Turbidity particles may adsorb other harmful contaminants. Turbidity particles known to be harmful themselves include asbestos, lead, bacteria and viruses, and protozoan cysts such as Giardia and Cryptosiporidium.

Water-quality standards and criteria are developed by the States, approved by the U.S. Environmental Protection Agency (USEPA), and then promulgated (passed into law) as standards by each State. Graphs on this website allow comparison of measured and computed data to these standards and criteria by plotting them as straight lines. When evaluating data to decide whether water quality is suitable for the intended use, viewers are cautioned to consider the uncertainty associated with these computed data.