Turbidity, to put it simply, is a measurement of clarity (i.e., transparency). The medium may seem foggy or murky when suspended particles, such as silt, algae, plankton, and sewage, are present. Instead of allowing light to pass through it directly, these particles scatter and absorb light waves. 

A greater turbidity rating denotes a cloudier, "thicker," and more particle-filled medium. The turbidity of the medium is low when it is clear.

In the majority of contemporary turbidimeters, a sample is collected, added to a vial, and then put within the apparatus. Then, photodetectors positioned 90 degrees from the sample shine the fixed light beam in its direction to measure how much light is transmitted and how much is dispersed.

As an alternative, you can bring a portable device to the sample, like our Photepette instrument. In order to take a reading, the users placed a CuveTip on the apparatus and inserted the tip directly into the sample, as seen in the illustration below: