Measurements · Water Quality
Salinity
Also known as salt content, PSU
Salinity derived from conductivity/temperature.
What it is
What is salinity?
Salinity is the concentration of dissolved salts in water, reported on the Practical Salinity Scale in practical salinity units (PSU), which for most purposes is equivalent to grams of salt per kilogram of water. Salinity is not measured directly but derived from conductivity and temperature: because dissolved salts are what carry current, a sonde calculates salinity from its specific conductance using an internationally agreed relationship. It is one of the defining properties of a water body, controlling density and stratification, the solubility of dissolved oxygen, and which organisms can live there.
Because it shapes so much of estuarine, marine, and aquaculture ecology, salinity is a core channel wherever fresh and salt water mix.
Health and operational effects
Aquatic organisms are adapted to a particular salinity range, and many can tolerate only a narrow band, so a shift stresses or displaces them. In estuaries, the tidal movement of the salt wedge governs where species live and breed, and unusual salinity (from drought, flood, or water withdrawal) can push that boundary and disrupt the ecosystem. Salinity also affects dissolved oxygen, because saltier water holds less oxygen, so the two are interpreted together. In aquaculture, salinity is controlled closely for the health of the stock. In agriculture, rising salinity in irrigation water reduces crop yields and damages soils. Where saline intrusion threatens a freshwater intake, salinity is the parameter that raises the alarm.
How it is measured
How Salinity Is Measured
Salinity is computed from conductivity and temperature rather than measured by its own sensor: the multiparameter sonde measures the water's specific conductance and applies the Practical Salinity Scale to convert it to PSU. That calculation is one channel of the sonde connected to a Thiamis gateway, sharing the conductivity cell and temperature sensor with the conductivity and specific-conductance readings. Its accuracy therefore depends on keeping that cell clean and calibrated, because biofouling and deposits distort the underlying conductivity and, through it, every derived salinity value; regular maintenance against drift is essential on estuarine and marine deployments where fouling is rapid.
An instrument on Thiamis5
A third-party instrument connected to a Thiamis gateway, reporting into the same Environet account.
Placing salinity sensors
Salinity is measured in-situ by the sonde, and where to place it depends on the question. In an estuary, salinity stratifies strongly (fresh water floats over denser salt water), so profiling or measuring at several depths reveals the salt wedge that a single reading would miss. Tidal and seasonal cycles mean continuous logging is essential to capture the full range and the timing of intrusion events, which a spot sample cannot represent. Because estuarine and coastal waters foul quickly, the sonde needs frequent cleaning and calibration checks to keep the conductivity-derived salinity trustworthy.
Every device and option that measures Salinity 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 Salinity
Each one links to the solution page showing what that industry measures it for.
Aquaculture & Fish Farming
Core parameterSalinity is a critical husbandry parameter in marine, brackish, and estuarine aquaculture, where species tolerate only a defined range and rainfall or evaporation can shift it quickly.
Water Quality Monitoring
Often addedRivers, lakes, drinking water, and stormwater
Related
More in Water Quality
Questions
Salinity FAQ
How is salinity measured if there is no salinity sensor?
Salinity is calculated, not measured directly. The sonde measures conductivity and temperature, converts them to specific conductance, and then applies the internationally agreed Practical Salinity Scale to report salinity in PSU. This is why the same conductivity cell provides conductivity, specific conductance, and salinity together.
What is the salinity of seawater?
Open ocean seawater is close to 35 PSU, which is roughly 35 grams of dissolved salt per kilogram of water. Freshwater sits near zero, and the brackish water of estuaries falls in between, varying with the tide and river flow.
Why does salinity matter for aquatic life?
Most organisms are adapted to a specific salinity range and are stressed by departures from it, so salinity determines which species live where, especially in estuaries. It also lowers how much dissolved oxygen the water can hold, so a rise in salinity can compound oxygen stress.
How do I monitor salinity?
Deploy a multiparameter sonde whose conductivity cell derives salinity, connected to a Thiamis gateway and logging continuously through the tidal cycle, with regular anti-fouling cleaning and calibration. Use the configurator to pair a logger with a sonde covering salinity alongside conductivity, specific conductance, dissolved oxygen, and temperature.
Monitor Salinity on the Record
Schedule a callConfigure Salinity Monitoring All parameters
A 30-minute call: you tell us about your application, then we demo the solution for it.