The objective of this research work was to determine the reliability of a electrochemical impedance spectroscopy method to determine the percentage of adulteration of milk with tap water. To measure the adulteration, the resistance in ohms was correlated with respect to the concentration of water in the milk. For this, a multichannel potentiostat was used. The milk was maintained at a temperature of 24 ° C. Five concentrations of tap water were used with respect to pure cow's milk, with values of 10, 15, 20, 25 and 30% v / v. A calibration curve was constructed from a sample of pure milk (unadulterated) as the reference standard. All readings were made by four repetitions at frequencies between 1 and 10000 hertz (Hz). From this, for each concentration of water in the milk through the Bode diagrams, a response of the resistance in ohms (Ω) was obtained as a function of the frequency (Hz). To determine the reliability of the method, linearity, precision, limit of detection and limit of quantification were determined. The linearity of the method was demonstrated from the coefficient of proportionality of 0.9975. The coefficient of variation (CV) had a value of 0.04%, which indicates that the accuracy of the method is acceptable. On the other hand, the limit of detection and limit of quantification correspond to values of 2.22 and 0.44% v / v respectively.