Water quality control is a critical task in environmental monitoring, industry, and medicine. This paper presents the development of a conductometric sensor designed to monitor NaCl concentration in aqueous media. The design of the sensor cell and the electrochemical principles underlying the measurements are discussed. A mathematical model is proposed that accounts for temperature effects, ion types, and the geometric dimensions of the sensor. The impact of alternating current on measurement accuracy is analyzed, along with temperature compensation methods utilizing thermistors. An improved approach to exciting active conductometric sensors is introduced, enabling accurate monitoring of ionic impurities. The AC excitation method, based on rectangular signals with cyclic polarity reversal, effectively suppresses constant errors, noise, and parasitic thermocouple voltages. This technique ensures high accuracy by minimizing radio frequency interference and thermal self-heating of the sensor. A functional diagram based on a bridge configuration is provided, detailing the operation of a transistor switch stage used to generate a symmetrical excitation signal. The advantages of AC over DC excitation are substantiated, particularly in terms of thermal stability, sensitivity, and measurement reliability. The developed sensor circuit enables precise determination of dissolved substance concentrations and avoids systematic errors associated with electrolysis under direct current. Calibration was performed using standard solutions, and the sensor’s metrological characteristics—including absolute, relative, and total measurement errors—were evaluated. The results confirm the high accuracy of the proposed system for water quality monitoring.