Which is not a measure for water turbidity?

The Siple turbidity unit is not commonly recognized as a standard measure for water turbidity. The accepted units used to measure turbidity include Nephelometric Turbidity Units (NTU), which are widely utilized in water quality assessments due to their effectiveness in quantifying light scattering properties of a water sample.

Formazin turbidity units are also relevant, as formazin is often used as a calibration standard in turbidity measurements, particularly for turbidimeters, which measure the scattering of light through a water sample.

Jackson turbidity units are another recognized method for quantifying turbidity, based primarily on a different measurement technique involving a standard glass jar and a visual comparison of a secchi disk.

In contrast, the Siple turbidity unit is not a standard measurement in water quality studies and is less frequently employed than the other units mentioned. Thus, it does not align with prevalent turbidity measurement practices.