The text of this international standard “Water quality; Determination of turbidity” is included in the German standard DIN 38404 Part 2 and its European version EN 27027. It describes two semi-quantitative methods (transparent cylinder, viewing disc) and two quantitative, optical methods, namely measurement of the scattered radiation and the transmitted radiation (Turbidity value, Scattered light). It also contains detailed directions for preparing the formazine solution and calibration of the turbidimeters.