Water Quality
Parameters
Turbidity
Turbidity is a measure of the cloudiness of water. It is used to indicate water quality and filtration effectiveness (e.g., whether disease-causing organisms are present). Higher turbidity levels are often associated with higher levels of disease-causing microorganisms such as viruses, parasites and some bacteria. These organisms can cause symptoms such as nausea, cramps, diarrhea, and associated headaches.

Turbidity measurements are of extreme importance in quality monitoring in water,
wastewater, beverage production, electroplating and petrochemical applications.
Light passing through liquid which contains undissolved solids, such as algae, mud,
microbes and other insoluble particles, is both absorbed and scattered.

Turbidity increases with the amount of undissolved solids present in the sample. However, the shape, size and composition of the particles also influence the degree of turbidity.

Turbidity has been determined by simply measuring light passing through the sample. Measuring the scattered light at an angle of 90° has proved to be a more accurate method particularly at lower measuring ranges. Instruments that use this method are also referred to as nephelometers.

Turbidity or nephelometers instruments differ by the light source they utilize. Infrared units (IR-LED) with a wavelength of 860 nm are required for methods: ISO 7027/ DIN EN 27027 (EN ISO 7027). Standard methods specifies the use of units that use white light by a tungsten wide-band lamp for water and wastewater analysis.

An infrared light source minimizes or even eliminates the influence of coloration in
a solution, because there is practically no absorption at a wavelength of 860 nm.
The detection sensitivity for small particles, on the other hand, is somewhat lower
at this wavelength because of the generally lower light scattering of small particles.

White light has a higher sensitivity for small particles, however the inherent
coloration of the solution has a stronger disturbing effect in this case.
The IR measurement is required by DIN ISO, the white light measuring by US EPA.

The nephelometric measuring with 90° scattered light is advantageous for the
lower turbidity range. In contrast, the transmittance method is better suited for
medium to high turbidities, where there are stronger light scattering and shadowing effects among the larger-sized particles. In this case, the diminution of light intensity gives a more accurate result then a 90° scattered light metering. Laboratory instruments for higher turbidity ranges therefore offer significantly more measuring options.