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Analytical · Glossary

What is Turbidity?

NTU, FNUAnalytical

Turbidity is the cloudiness of water caused by suspended particles, measured by how much light they scatter.

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Turbidity Explained

Nephelometers measure light scattered at 90°. NTU is used with white light (US EPA 180.1); FNU with infrared light (ISO 7027).

Bubbles, colour and window fouling cause errors; online analysers use debubbling and automatic cleaning.

Turbidity: Typical Values

Drinking water targetoften below about 1 NTU
Calibration standardformazin or stabilised polymer standards
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Calculators for Turbidity

CalculatorDilution CalculatorFree online calculator with formula and worked example.

Frequently Asked Questions

What is Turbidity?

Turbidity is the cloudiness of water caused by suspended particles, measured by how much light they scatter.

NTU or FNU?

They read similarly on formazin but differ on real samples; report the unit of your method.

Is turbidity the same as suspended solids?

No, but they can be correlated for a given water.

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