Turbidity of Drinking Water

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Pick up a glass of water and hold it to the light. Can you see any finely divided, insoluble particles suspended in the water? Or does the water seem hazy? If so, the water is turbid.

Turbidity. Turbidity and suspended matter are not synonymous terms, although most of us use the terms more or less interchangeably. Correctly speaking, the suspended matter is that material which can be removed from water through filtration or the coagulation filtration process. Turbidity, on the other hand, is a measure of the amount of light scattered and absorbed by water because of the suspended matter in the water.

There is also some danger of confusion regarding turbidity and color. Turbidity is the lack of clarity or brilliance in water. Water may have a great deal of color -- it may even be dark brown -- and still be clear and without suspended matter.

Turbidity - Low	Turbidity - High

When water has a large amount of such suspended particles, we lose our zest for it. While high-turbidity water may be safe to drink, it seems offensive to us. The EPA Interim Primary Drinking Water Regulations recommend that the turbidity of potable water be less than 1 unit and less than 5 units under special conditions. The suspended particles clouding the water may be due to such inorganic substances as clay, rock flour, silt, calcium carbonate, silica, iron, manganese, sulfur, or industrial wastes. Again, the clouding may be caused by organic substances such as various microorganisms, finely divided vegetable or animal matter, grease, fat, oil, and others.

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