Test Method Technical Information


Tests For: Turbidity in Natural and Treated Waters
Tests Range: 5–400 Turbidity Units
Reagent Chemistry Used: No reagents, 180° Attenuated turbidity
Basis of Test Method: Standard Method 2130-B

Testing for Turbidity

Turbidity is an important parameter for characterising water quality. Turbidity is caused by the scattering of light by suspended matter such as clay, silt, finely divided organic and inorganic matter. A knowledge of turbidity facilitates estimation of the concentration of undissolved substances.

For a higher level of accuracy, the Turbimeter Plus instrument should be used. The recommendation is that turbidity measurement is best carried out using a nephelometric measurement technique at levels below 40 NTU. Above 40 NTU the recommendation is to measure also at 180° to ‘compensate’ the 90° readings. The Turbimeter Plus uses an optical system which provides dual measurement for both nephelometric and compensated channels, giving greater accuracy at lower turbidity levels.

Reagent Chemistry

The turbidity of the water is determined photoelectrically using the Palintest Photometer. In many samples both colour and turbidity will be present. To separate the effect of turbidity and colour, the sample is compared against a filtered portion of the same water.

The Palintest method has been calibrated against the widely recognised formazin turbidity solutions. Turbidity is expressed in terms of Formazin Turbidity Units (FTU). These units are broadly equivalent to Jackson Turbidity Units (JTU) and Nephelometric Turbidity Units (NTU).