Conductivity is the ability of a material to transmit energy in the form of electricity or heat. In water quality terms, it indicates how much conductive material is in the water. The higher the conductivity measurement, the more conductive material is in the water.
The standard unit of measure for conductivity is Siemens per meter (S/m).
The siemens (symbol: S) is a unit of electric conductance and electric admittance. Conductance and admittance are the reciprocals of resistance and impedance respectively, hence one siemens is equal to the reciprocal of one ohm, and is sometimes referred to as the mho. It is named after the German inventor and industrialist Ernst Werner von Siemens. In English, the term siemens is used both for the singular and plural.
When testing water quality for conductivity measurements, you will hear terms like microsiemens, micromhos, millisiemens, and millimhos.
-Microsiemens (uS) is the same as the micromhos (umhos).
-Millisiemens (mS) is the same as millimhos (mmhos).
These units of measure operate the same way as metric distance measures. The meter is short and the kilometer is long, but they both measure distance. Microsiemens and millisiemens work the same way. 1 millisiemen is equal to 1000 microsiemens.
Different materials conduct electricity differently – this principle applies to dissolved materials, as well. If you have a tablespoon of sodium chloride (table salt) and dump it in a glass of pure water, then take another tablespoon of potassium chloride salts and dump it in another glass of pure water, the conductivity measurements from the two glasses will be different.
Some typical conductivity measurements of water:
Ultra pure water: 0.05 – 1.0 microsiemens
Drinking water: 200 – 500 microsiemens
Seawater: 30,000 – 50,000 microsiemens
It is important to use a conductivity meter that can test different salt types and properly compensate for temperature differences in order to get the most accurate conductivity measurements.
To learn about Conductivity vs. TDS, check out this blog post: http://blog.myronlmeters.com/archive/5