What it is
Turbidity is a measure of the fine particles suspended in water, which scatter light and make it look cloudy or dull. It is reported in nephelometric turbidity units (NTU). Clear drinking water is usually below 1 NTU.
Where it comes from
Particles come from silt and clay washed into a source after rain, from iron or manganese that has come out of solution, from disturbed sediment in a tank or borehole, and from corrosion or biofilm in pipework. A sudden rise in turbidity often follows heavy rain or work on the supply.
Why it matters
Turbidity is not harmful in itself, but it matters for two reasons. Particles can shelter bacteria from UV light and chlorine, so disinfection may not work properly when water is cloudy. And a rise in turbidity is often the first visible sign that surface water is getting into the supply.
What can be done about it
Sediment filtration ahead of any UV unit is the usual fix, sized to the particle load. Where turbidity comes from iron or manganese, treating those solves it. The engineer will also look at the source protection, because a well or spring that lets in silt is letting in other things too.
Information last reviewed 5 October 2026 by Pozzani Pure Water.