Some of the common units of conductivity are microsiemens or millisiemens per centimeter, as well as micromhos or millimhos per centimeter. One siemen is equal to one Mho when measuring conductivity.
Conductivity is water's ability to allow the flow of electricity and is defined as the reciprocal of resistivity, which is water's opposition to the flow of current. Water's conductivity is directly proportional to the amount of ions in the water. The more ions in the water, the higher the level of conductivity. Ions come from broken-down electrolytes such as salt, chlorides, alkalis and carbonate compounds. When these electrolytes split, they become either positively or negatively charged ions, which are conductors and dictate how efficiently water is able to allow the flow of electrical current. Deionized water can act as an insulator, whereas saltwater is highly conductive of electricity.