Measurements · Water Quality
Turbidity
Also known as water clarity, NTU
Water turbidity (light scattering by suspended particles).
What it is
What is turbidity?
Turbidity is a measure of the cloudiness of water (how much suspended material scatters light rather than letting it pass through), reported in nephelometric turbidity units (NTU). The particles responsible include silt and clay, plankton, organic debris, and fine matter stirred up by flow or discharge. Turbidity is not a measure of any specific substance but of clarity, and it is one of the most widely used water-quality parameters because it responds quickly, is easy to measure continuously, and correlates with a range of problems from sediment pollution to failing filtration. It is closely related to total suspended solids (TSS): turbidity is the optical clarity measurement, and a site-specific relationship is often used to translate it into an estimated TSS concentration.
Because it reacts fast and reveals so much about what is entering a water body, turbidity is a mainstay of river, reservoir, and drinking-water monitoring.
Health and operational effects
High turbidity harms aquatic ecosystems in several ways: suspended sediment blocks the light that plants and algae need, smothers spawning gravels and the eggs and invertebrates within them, and clogs the gills of fish. The particles also carry attached pollutants (nutrients, metals, and pathogens), so a turbidity spike often marks the arrival of contamination as well as sediment. In drinking-water treatment, turbidity is a critical control parameter because particles shield microorganisms from disinfection and indicate whether filtration is working, which is why treated-water turbidity is watched continuously.
Limits
Turbidity Limit Values
The published values, by averaging period; each links to the standard that sets it.
Treated water
- EPA drinking water 1 NTU: ≤0.3 NTU in 95% of samples
Turbidity is reported in NTU. Drinking-water treatment sets strict turbidity limits on filtered and treated water, while environmental criteria for natural waters are often expressed as a permitted increase above background rather than a fixed ceiling. The applicable values appear in the limit table on this page. Interpret turbidity against its baseline and its events: a stable low value is the healthy norm, and the informative signals are the sharp peaks following rain or disturbance and any sustained rise. Where a local turbidity-to-TSS relationship has been established, the reading is also a continuous estimate of suspended-solids concentration.
How it is measured
How Turbidity Is Measured
Turbidity is measured with a nephelometric sensor, which shines a beam of light into the water and measures the light scattered by suspended particles at an angle, usually ninety degrees; more particles scatter more light and give a higher NTU reading. The sensor is one channel of a multiparameter sonde connected to a Thiamis gateway. Optical turbidity sensors are especially vulnerable to biofouling and to bubbles and debris on the optical window, all of which inflate readings, so many use a mechanical wiper and all require regular cleaning and calibration against a turbidity standard to counter drift over a deployment.
An instrument on Thiamis5
A third-party instrument connected to a Thiamis gateway, reporting into the same Environet account.
Placing turbidity sensors
Turbidity is measured in-situ by the sonde at a representative point in the flow, positioned to avoid trapping debris or sitting in a stagnant pocket where particles settle out. Because turbidity can rise and fall within minutes of a rainfall or discharge event, continuous logging with alarms is essential to capture the peak, which a routine grab sample would almost always miss. Siting the optical window where it stays clean, and using a wiper where fouling is heavy, keeps readings trustworthy; regular calibration against a standard maintains accuracy through the deployment.
Every device and option that measures Turbidity 5
| Device / option | Type | Base platform | Measures |
|---|---|---|---|
 YSI · EXO1, EXO1S, EXO2… | Water Quality Sondes | Thiamis | |
 In-Situ · Level TROLL 300, Level TROLL 400, Level TROLL 500… | Water Quality Sondes | Thiamis | |
 Eureka Water Probes · Manta+ 20, Manta+ 25, Manta+ 30… | Water Quality Sondes | Thiamis | |
 Spectra Scientific · Spectra Litmus 6, Spectra Litmus 4 | Water Quality Sondes | Thiamis | |
 YSI · 6600 V2, 6600EDS V2, 6920 V2… | Water Quality Sondes | Thiamis |
Where it is monitored
Solutions That Monitor Turbidity
Each one links to the solution page showing what that industry measures it for.
Water Quality Monitoring
Core parameterTurbidity, the cloudiness caused by suspended particles, is the water-quality parameter that responds fastest and most visibly to storms, spills, dredging, and treatment upsets.
Aquaculture & Fish Farming
Often addedDissolved oxygen, temperature, and ammonia control
Hydrology, Level & Flow
Often addedFlood warning, stream gauging, and groundwater
Article Library
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Questions
Turbidity FAQ
What is the difference between turbidity and TSS?
Turbidity is an optical measure of how cloudy water is, reported in NTU, while total suspended solids (TSS) is the actual mass of suspended particles in milligrams per liter. Turbidity is fast and easy to measure continuously; TSS is more laborious but is a true concentration. A site-specific correlation is often used to estimate TSS from continuous turbidity.
What causes turbidity to spike?
Usually rainfall and the runoff, erosion, and resuspension it drives, but also dredging, construction, algal growth, or a discharge. Because these events can raise turbidity within minutes and fall away again quickly, the peak is easy to miss with spot sampling and best captured by continuous logging.
Why does turbidity matter for drinking water?
Because suspended particles shield microorganisms from disinfection and indicate whether filtration is performing, turbidity is a front-line safety parameter in water treatment. A rise in treated-water turbidity can mean that pathogens are passing through, so it is monitored continuously against tight limits.
How do I monitor turbidity?
Deploy a multiparameter sonde with a nephelometric turbidity sensor (ideally with a wiper) connected to a Thiamis gateway, logging continuously with alarms and regular cleaning and calibration. Use the configurator to pair a logger with a sonde covering turbidity alongside TSS, chlorophyll, dissolved oxygen, and temperature.
Monitor Turbidity on the Record
Schedule a callConfigure Turbidity Monitoring All parameters
A 30-minute call: you tell us about your application, then we demo the solution for it.