Guide to measuring turbidity in water

Turbidity is a measure of how cloudy water is. There are many methods to measure turbidity. The best way would in a wide variety of samples is with a nephelometer – also known as a turbidity meter. turbidity meters utilise a light and photo detector to measure light scatter, and read out in unit of turbidity, such as nephelometric turbidity units (NTU) or formazin turbidity units (FTU).

Turbidity is an optical property of liquid that causes light to be scattered and absorbed, not transmitted. It is the ‘cloudiness of water’. Turbidity is caused primarily by suspended solids. It is not a measurement of suspended solids (in literature as TSS total suspended solids). Density is used to measure suspended solids. Turbidity is related to the size of particles, not density.

EPA meters

Method:

Uses a tungsten lamp
Takes a measurement at 90° from the light source
Maximum cuvette distance is 10 cm
Focuses on NTU ratings below 40 NTUs

Bench meters:

HI88703
HI83414 (in addition also measure free & total chlorine)

Portable meters:

HI98703
HI93414 (Also measures free and total chlorine)
HI93102 (For pools and spas; not municipalities; log memory 25 readings). Also measures free and total chlorine, bromine, iodine, iron, and cyanuric acid

ISO meters

Method:

Uses an infrared LED at 860nm
The total bandwidth cannot be greater than 60nm
Recommends a 90° measurement at NTU less than 40, and a direct beam 180° measurement at values higher than this

Bench meters: