This International Standard specifies four methods for the determinations of turbidity of water.
Section 2 specifies semiquantitative methods, employed for example in field work:
a) method using the transparency testing tube (suitable for pure and lightly polluted water);
b) method using the transparency testing disk (especially suitable for surface water).
Section 3 specifies quantitative methods using optical turbi-dimeters:
a) method by measuring diffused radiation, applicable to water of low turbidity (for example drinking water). Depen-ding on the instrument design, it may also be used for waters of higher turbidity;
b) method by measuring the attenuation of a radiant flux, more suitable for highly turbid waters (for example waste or polluted waters).
Measurements of turbidity can be affected by the presence of dissolved light-absorbing substances (substances imparting colour). Such effects can be minimized, however, by perform-ing measurements at wavelengths greater than 800 nm. Only a blue colour, which may be found in certain polluted waters, slightly affects measurements of turbidity in this region of the spectrum. Air bubbles may also interfere with measurements but such interference may be minimized by careful handling of the samples.