Turbidity is the amount of cloudiness in the water. Turbidity can be caused by; silt, sand and mud, bacteria and other germs, or chemical precipitates.

It is important to measure the turbidity of domestic water supplies, as these supplies often undergo some type of water treatment which can be affected by turbidity. High turbidity will also fill tanks and pipes with mud and silt, and can damage valves and taps. Where chlorination of water is practised, even quite low turbidity will prevent the chlorine killing the germs in the water efficiently.