NTU (Nephelometric Turbidity Units)
The standard unit for measuring turbidity (cloudiness) in water.
NTU stands for Nephelometric Turbidity Units. It is the standard unit for expressing turbidity — how cloudy or hazy water is due to suspended particles.
How it works
A nephelometer shines a light beam through a water sample and measures the amount of light scattered at a 90-degree angle. More scattered light = more suspended particles = higher NTU reading.
Scale reference
| NTU | Description |
|---|---|
| <0.5 | Very clear (typical treated drinking water) |
| 0.5–1 | Clear |
| 1–5 | Slightly hazy |
| 5–50 | Noticeably cloudy |
| 50+ | Very turbid (muddy) |
ADWG guideline
The ADWG sets 5 NTU as the aesthetic guideline. Most Australian water treatment plants target well below 1 NTU in their output.
Related Terms
Check Your Water
See how ntu (nephelometric turbidity units) levels compare in your suburb with real water quality data.
Disclaimer: Glossary definitions are provided for general educational purposes only and do not constitute medical advice or professional guidance. For specific health concerns about your drinking water, consult a qualified health professional. See our Terms of Use.