scope:

Specifies four methods for the determination of turbidity of water. Two semiquantitative methods, employed for example in field work, are specified: a) measurement of turbidity using the transparency testing tube (applicable to pure and lightly polluted water); b) measurement of turbidity using the transparency testing disk (especially applicable to surface water). Two quantitative methods using optical turbidimeters, are specified: c) measurement of diffuse radiation, applicable to water of low turbidity (for example drinking water); Turbidity measured by this method is expressed in formazin nephelometric units (FNU); results typically range between 0 FNU and 40 FNU. Depending on the instrument design, it may also be applicable to waters of higher turbidity. d) measurement of the attenuation of a radiant flux, more applicable to highly turbid waters (for example waste or polluted waters). Turbidity measured by this method is expressed in formazin attenuation units (FAU), results typically range between 40 FAU and 4000 FAU.