Conductivity of water

Measuring the resistance of ordinary water by comparing it with a known resistance, is explained here. For ionic solutions measuring the DC resistance gives error, due to electrolysis and formation of gas bubbles at the electrodes. The AC voltage from SINE is connected to GND via a 10kOhm resistor. The black trace is the total voltage and the red one is the voltage across the 10k resistor.

Total voltage Vt = 3.25 V

Voltage across 10k = 2.6 V

Current = 2.6 / 10000 = 0.26 mA

Voltage across the electrodes = 0.65

Resistance offered by the solution = 0.65 / .00026 = 2500 Ohms