Conductivity, Salinity and TDS

November 20th, 2018

Conductivity, Salinity, TDS

Conductivity is a measure of the water’s ability to conduct electricity

Salts and other inorganic chemicals form electrically charged particles called ions

Pure water is a poor conductor of electricity

Conductivity is a measure of the ionic strength of water


Conductivity is usually reported as specific conductance – temperature compensated conductivity to 25 °C

Conductivity probes detect the AC resistance between two electrodes

Salinity is then calculated from this conductivity value

Salinity is the total concentration of all dissolved salts in water

The most common ions in sea water (chloride, sodium, magnesium, sulfate, calcium, potassium, bromine)

Total dissolved solids (TDS) combine the sum of all ion particles that are smaller than 2 microns

EPA recommends an upper limit of 500 mg/L TDS

Units of measure

Salinity –  ppt

Conductivity – mS/cm &  uS/cm

TDS –  mg/L


The higher the dissolved salt concentration, the higher the density of water. This increase in density with salt levels is one of the driving forces behind ocean circulation

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