What is Turbidity?

Turbidity is the name given to define the “cloudiness” or “haziness” of a given fluid. This haziness is usually caused by suspended solids present in the liquid, which are often invisible to the naked eye in their individual form but which can be seen by their collective presence and the cloudiness it engenders. The term itself is not a defining one; it does not identify or quantify what is actually present in the water, only that some substance is giving it discolouration.

Indeed, almost all water contains some manner of suspended solids. Normally, these contain enough density to sink to the bottom of the container, allowing the fluid to retain its transparency – these solids are known as settleable. However, when the solids are smaller in size and less dense than the water itself, they will take much longer to sink to the bottom and thus discolour the water. These ones are known as colloidal.

While turbidity is normally applied to water, it can be used to describe all manner of liquids, as well as transparent solids such as glass and plastic as well.

How is Turbidity Caused?

Turbidity comes about via a number of different reasons, depending on the source of the liquid and its recent history. Some of the possible causes of turbidity and discolouration include:

• Sudden changes in pressure of a pipeline – for example, when firefighters turn on a water hydrant to combat a blaze, when leakages occur or when industrial strength cleaning equipment is used.
• Natural discolouration via the daily processes of microscopic organisms such as phytoplankton.
• Erosion, effluence and run-off from urban and industrialised areas.
• Heavy industry resulting from agriculture, mining or construction can alter sediment levels in soil and thus indirectly affect turbidity of nearby water supplies.
• Storm water run-off can infiltrate water supplies too and cause discolouration.

Why is Turbidity a Problem?

In terms of our drinking water, the more turbid a fluid is, the more likely are the chances that those who consume it will develop gastrointestinal complications. The suspended solids found in the water can be preyed upon by viruses and bacterium, who cling to them and find their way into our bodies through the ingestion of the turbid water.

Meanwhile, in terms of other animal and plant life, a turbid river or lake can severely affect the flora and fauna inhabiting the water. If sunlight is prevented from reaching the depths of the water by the existence of suspended solids, the lower-lying plants and animals can have their growth inhibited. Fish, in particular, can find their oxygen intake capacity impeded by overly turbid waters.

How Can We Measure Turbidity?

In a bid to combat high levels of turbidity in our bodies of water, the UK water industry has been forced to comply with 27 different regulatory measures, one of which focuses on turbidity. If companies exceed the allowance of turbidity in their water, they will receive fines of £1,000 for every consumer complaint. As such, allowing their water to become severely cloudy can be a costly business, and one which they are keen to avoid by monitoring turbidity levels regularly.

The most common units of measurement for turbidity are Nephelometric Turbidity Units, and 95% of all companies now use the ground-breaking technology NephNet to achieve their objectives. For more information why this technology has such a stranglehold on the market, how it differs from previous methods and a more in-depth look at turbidity in general, see the article Why a New Portable Turbidity Monitor is Revolutionising the Water Industry.