Turbidity can be said to be as a result of the presence of different varying size of particles. These particles, scatter and absorb light. This gives the material being considered a cloudy or milky appearance. It is therefore clear that, the turbidity in a material is caused by the particles found suspended in the material. Some of these particles include; sludge, particles of limestone and in some cases, some microorganisms.

Initially, people tried to use visual machines to try and measure the turbidity level in materials. Some units such as the Jackson Turbidity Units, also known as the JTU were formed being founded on the volume of silicic acid which was dissolved in some materials which were known as the diatomaceous earth. This material was usually found in water. An instrument known as the candle turbidity analyzer was used to measure the turbidity. The instrument was made up of a candle and some sort of a glass vessel. The glass vessel allowed for people to visually observe and compare the suspension against the solution of the silicic acid.

With passage of time, still today people use an apparatus known as the ‘sight disk’ which is white in color. This apparatus is made up of bronze. What happens is that, the disk is usually fully immersed into the water. Care should be taken to make sure that the disk is not left visible from above. The depth of immersion is then used as the basis of measuring the turbidity. In the current age, turbidity is usually measured using turbidity meters. The meters are also commonly referred to as the optoelectronic turbidity meters. While using these meters, an artificial light source is used. The light source then emits some light on the material being measured. The intensity of the light being used must be known prior to this experiment.

The light is usually scattered or absorbed by the usually suspended particles in a material sample. If some light is scattered, it is usually detected by a photodetector which then records it. The turbidity meter usually scatters the light at an angle of 90 degrees. The turbidity meter usually relies on a principle commonly known as the nephelometry, which is a measurement principle. From this principle, an instrument known as the nephelometer was invented. It is an example of a turbidity analyzer that can measure the scattered light, usually at a 90-degrees angle. The turbidity analyzers are normally calibrated and marked to help users obtain tangible results. The turbidity meters are usually adjusted and altered using solutions of formazine.

Usually, measurements taken by the use of the turbidity meters are always recorded in units known as the Formazine Nephelometric units or simply commonly referred to as the FNUs. Something important to note here is that, usually the results obtained by measurement using a meter that operates on this principle of light transmission is by standard shown in units known as the FAUs or the Formazine Attenuation Units. These units are the standard ones and are widely known and accepted as the units for measuring turbidity.