Turbidity Measurements – What do they mean?

Turbidity, simply put, is the measure of cloudiness in a liquid. For our purposes, this liquid is generally water. It is one of the most basic qualities of water but also one of the most intuitive, as turbidity says a lot about water quality, as a whole. When we think of water quality we pretty much default to the clarity of our water – the clearer the water is, the safer it is, whether it’s for drinking, washing, wastewater, etcetera. Turbidity can be impacted by many different sorts of particles in the water; soil, algae, minerals, oils, or bacteria to name a few.

There are standards of turbidity that need to be met during water treatment at several stages which helps determine efficiency while also helping to maintain government quality standards. To measure turbidity, we must measure the ability of light to pass through the water; the higher the turbidity reading, the more particles that are suspended in the water. Turbidity is measured in NTU’s, or nephelometric turbidity units.

We know what turbidity is, now we need to learn how it is measured. Some methods are more rudimentary than others. The Secchi disk, for example, is one method for gaining a quick idea while in the field. It isn’t the most exact measurement of turbidity, however, and should not be used when determining quality when meeting compliance standards. This is when you may want to use something more refined, like a turbidity meter. This machine is more expensive and requires some upkeep, but essentially you can easily take a sample of water and get an accurate NTU reading within a few seconds. If you maintain a regular calibration schedule and are sure to clean out our sampling tubes regularly, a turbidity meter provides an accurate reading of turbidity in the water.

It is also important to use correct technique when taking water samples to use in the turbidity meter. An improperly gathered sample can lead to a skewed reading. Turbidity testing can be a requirement during the pre-construction process, or potentially for the duration of a site’s dewatering activities. Be sure to maintain the proper log and reports for all turbidity testing. This includes ensuring your SWPPP contains all applicable information! KCI offers professionals in the field to conduct your testing for you as needed, as well as high quality equipment that can be rented if you are familiar with the process and wish to do your own testing.

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