Conductivity is formally defined as the reciprocal of resistivity, which is worth elaborating on 3. Resistivity is a measurement of water’s opposition to the flow of a current over distance. Pure water has a resistance of 18.2 Mohm*cm 5. Resistivity decreases as the ionic concentration in water increases. A fun way to remember that resistivity and conductivity are reciprocals (1/measurement) is in the unit name – mho and ohm are the same letters, in reverse.
