Measurements · Water Quality
Chloride
Also known as chloride ion
Chloride ion concentration in water.
What it is
What is chloride?
Chloride is one of the most abundant dissolved ions in natural water, reported in milligrams per liter. It is a highly mobile, conservative ion: it does not readily react, precipitate, or degrade, so once it enters water it tends to stay there. It occurs naturally from the weathering of rocks and from seawater, but its concentration is often driven by human sources: road de-icing salt, water softeners, sewage, industrial effluent, and saline intrusion. Because it tracks salinity and moves conservatively, chloride is a useful tracer of pollution and of fresh- and salt-water mixing. It also contributes directly to conductivity. Because it fingerprints road salt, sewage, and saline intrusion, chloride is a useful channel in river, groundwater, and drinking-water monitoring.
Health and operational effects
Chloride is not usually a direct health hazard at the levels found in fresh water, but it has real consequences. High chloride gives water a salty taste and accelerates the corrosion of pipes and infrastructure, which is why it carries a drinking-water guideline based on taste and corrosivity. In freshwater ecosystems, rising chloride (often from winter road salt washing off the land in cold-climate cities) stresses organisms adapted to low-salinity water, and it is an increasing concern as urban salt use grows.
Limits
Chloride Limit Values
The published values, by averaging period; each links to the standard that sets it.
Secondary
Chloride is reported in milligrams per liter. Drinking-water frameworks set a guideline for chloride based on taste and corrosivity rather than acute toxicity, and aquatic-life criteria set limits to protect freshwater organisms. Both are summarized in the limit table on this page. Interpret chloride as a conservative tracer and a trend: because it does not degrade, a sustained rise points clearly to a source such as road salt, sewage, or intrusion, and reading it alongside conductivity and salinity shows whether chloride is driving a broader change in dissolved salts. As with any ion-selective measurement, occasional laboratory checks anchor the record.
How it is measured
How Chloride Is Measured
Chloride is measured in-situ with an ion-selective electrode (ISE) on a multiparameter sonde connected to a Thiamis gateway: the electrode develops a voltage in proportion to the chloride-ion activity in the water, giving a continuous reading. Because chloride is a major contributor to conductivity, its reading is often interpreted alongside the conductivity and salinity channels, which respond to the same dissolved salts. Ion-selective electrodes drift and are subject to interference from other ions and to biofouling. The chloride sensor needs regular cleaning and calibration against standard solutions and is temperature-compensated. Electrode drift is the main thing to manage on a long deployment.
An instrument on Thiamis5
A third-party instrument connected to a Thiamis gateway, reporting into the same Environet account.
Placing chloride sensors
Chloride is measured in-situ by the sonde at a representative, well-mixed point: downstream of an urban catchment to capture road-salt runoff, near a coastal aquifer or intake to watch for saline intrusion, or below an effluent outfall as a tracer. Because road-salt and intrusion signals are seasonal and event-driven, continuous logging captures the winter pulses and the slow creep of intrusion that spot sampling would miss. Reading chloride together with conductivity and salinity confirms whether a change reflects general dissolved-salt loading or a specific chloride source. Regular cleaning and calibration keep the ion-selective electrode reliable against drift and fouling.
Every device and option that measures Chloride 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 Chloride
Each one links to the solution page showing what that industry measures it for.
Water Quality Monitoring
Often addedRivers, lakes, drinking water, and stormwater
Related
More in Water Quality
Questions
Chloride FAQ
Why is chloride a useful pollution tracer?
Chloride is conservative (it does not react, precipitate, or break down), so once it enters water it persists and simply dilutes downstream. A chloride signal that stays elevated therefore reliably fingerprints a continuing source such as road salt, sewage, or saline intrusion. That makes it a clear tracer of pollution and of fresh-and-salt-water mixing.
Where does chloride in fresh water come from?
Naturally from rock weathering and seawater, but often from human sources: winter road de-icing salt, water softeners, sewage, industrial effluent, and saline intrusion into aquifers. In cold-climate cities, road salt is a major and growing contributor that raises chloride in rivers and groundwater.
How is chloride related to conductivity and salinity?
Chloride is one of the main ions that carry electric current, so it contributes directly to conductivity and to the salinity derived from it. A chloride rise usually shows up in the conductivity and salinity channels too, and reading them together distinguishes a specific chloride source from a general change in dissolved salts.
How do I monitor chloride?
Deploy a multiparameter sonde with a chloride ion-selective electrode connected to a Thiamis gateway, logging continuously with regular cleaning and calibration and occasional laboratory checks. Use the configurator to pair a logger with a sonde covering chloride alongside conductivity, salinity, nitrate, and temperature.
Monitor Chloride on the Record
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