Which is the standard measure for water turbidity?

The standard measure for water turbidity is the Nephelometric Turbidity Unit (NTU). This unit is widely used because it is based on the principle of light scattering, specifically how light is scattered by suspended particles in water when illuminated at a particular angle. The NTU measurement provides a reliable and consistent way to quantify the turbidity of water samples.

The use of NTUs is supported by standardized testing methods, such as those established by organizations like the American Public Health Association (APHA) and the Environmental Protection Agency (EPA). This makes NTU the universally accepted standard for assessing water quality in various applications, including drinking water treatment and environmental monitoring.

Other units, such as the Siple turbidity unit, Formazin turbidity unit, and Jackson turbidity unit, have been historically used but are less common in contemporary practice. While Formazin is a common reference material for calibrating measurements, particularly in NTU, it is not a standalone measure. The Jackson turbidity unit, originating earlier in the field, is also largely historical and not used as a standard in modern laboratory analyses.