Electrical conductivity

Last changed: 19 February 2018

Electrical conductivity in water

The electrical conductivity, or specific conductance, in an aqueous solution depends on the concentration of dissolved ions, which is important both chemically, as it determines how different elements behave in the water, and biologically, since all aquatic organisms are dependent on the amount of dissolved ions in the surrounding water (due to e.g. osmosis). High conductivity, i.e. a large concentration of dissolved ions in the water, in general indicates weathering-susceptible soils or other types of influence from the surroundings. A periodic increase in conductivity in the deeper parts of a lake can indicate leakage of ions from sediment, usually as a result of anoxia.

Electrical conductivity constitutes the inverted value of the specific resistance of water, which may be defined as the resistance (ohm or Ω) in a water column with a length of 1 cm and an area of 1 cm2.

 

 

Known issues in the databases

The results derived from measurements at the currently used water temperature 25°C (since 1984) and the older measurements at 20°C are separated in the database, as the ion activity changes with temperature (ca. 2-2.5% per °C). The units also differ between the two methods of measurement. The unit currently used is the SI unit mS/m (actually S/m, but mS/m gives more manageable values), while the older method used µS/cm.

1 mS/m = 10 µS/cm

Current method of measurement

Valid since January 2002
Method: SS-EN 27 888-1 (ISO 7888:1985).
Instruments: Radiometer CDM 210 Conductivity Meter with flow-through cell detection unit CDC 511T 4 pol. Peristaltic pump Alitea with pump rate 10 ml/min. Haake thermal bath. Conductivity is measured at 25°C and given in mS/m.

Previous methods

1977-05 – 2001-12
Method: SS-EN 27 888-1.

Instruments: Radiometer CDM 83 Conductivity Meter with a flow-through cell detection unit. Peristaltic pump Alitea with pump rate 10 ml/min. Haake thermal bath. Conductivity is measured at 25°C and given in mS/m.

1984-01 – 1997-04
Method: Swedish Standard SIS 02 81 23
Instruments: Radiometer CDM 83 Conductivity Meter with flow-through cell detection unit. Peristaltic pump Alitea with pump rate 10 ml/min. Haake thermal bath. Conductivity is measured at 25°C and given in mS/m.

Older methods measuring at 20°C (unit µS/cm)
1982-01 – 1983-12
Method: Instrument manual.
Instruments: Radiometer CDM 83 Conductivity Meter. Flow-though cell. Water bath 20°C.

1968-01 – 1981-12
Method: Instrument manual.
Intruments: Kemotron Teramatic MHO 03. Direct reading instrument. Flow-though cell. Water bath 20°C.

1965-01 – 1967-12
Method: Wheatstone bridge. Conductivity is given as ×106 at 20°C.


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