When measuring the conductivity of water, it is related to the resistance value of water. The resistance value is large, the conductivity is poor, and the resistance value is small, the conductivity is good. According to Ohm’s law, at a constant water temperature, the resistance R of water is inversely proportional to the vertical cross-sectional area F of the electrode and proportional to the distance L between the electrodes. If the cross-sectional area F of the electrode is made 1 cm2, and the distance L between the two electrodes is 1 cm, then the resistance value is equal to the resistivity.
The resistivity of water is related to the amount of salt in the water, the concentration of ions in the water, the number of charges of ions, and the speed of movement of ions. Therefore, the resistivity of pure water is very large, and the resistivity of ultrapure water is even greater.