Turbidity

Figure 1. A highly turbid water stream.

Turbidity is a measure of the particles in water, particularly how much the material present in the water disrupts the passage of light. These suspended particles are generalized as sediment, which include various types of matter including soil particles, algae, plankton and microbes. These particles are extremely small, and can change the color of the water.

Turbidity is a measure of water clarity, as it is the observable characteristic of the extent that the suspended particles in the water impair the ability to see clearly through it. A nephelometer (Figure 2) is used in water treatment plants to measure turbidity, which measures light scattered within a section of water. In lakes, turbidity may be measured by use of a secchi disk (Figure 3), which is released into water until it can no longer be seen, at which point the depth of it is measured.

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  Figure 2. A nephelometer.

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  Figure 3. Secchi disk for measuring turbidity.

Importance and Impacts

Water temperature

High turbidity increases water temperature due to the particles absorbing sunlight. This is worrisome because higher temperatures of water result in less oxygen content, leading to hypoxic conditions. Suspended particles also scatter light, preventing it from reaching plants and algae, thereby further reducing oxygen content. These higher temperatures lead to fish using more oxygen due to increased metabolic rates as well, limiting the supply even more so.

Drinking water

Knowledge of water's turbidity is important and is closely monitored in water treatment facilities. Most particles that contribute to turbidity are not harmful to humans upon ingestion, however their content in water is an indicator to other substances that do cause harm. Measurements of turbidity give an indication of how well the treatment processes are working and allow for optimal selection in treatment technologies.

See water quality degradation for more information on the effects of substances within water.