Conductivity

Conductivity is the ability of water to conduct electricity.  This conduction requires ions in the water to be charge carriers.  Pure water contains no ions (aside from the occasional rogue water molecule), and so is a very poor conductor of electricity.  But as water picks up chemical salts, those salts add ions to the water when they dissolve.  So as the ionic strength of the water rises, so does conductivity - the “saltier” the water, the higher the conductivity.