A system and related method are provided for measuring conductivity/resistivity of water having high purity, including a temperature sensor and a conductivity/resistivity sensor exposed to a water source. The system further includes a computing assembly configured to receive measurement signals from the sensors and to determine change in resistivity over a change in temperature (a collected R/T slope) from the collected temperature measurements and the collected resistivity measurements. The system compares the collected R/T slope to a standardized R/T slope at a temperature value corresponding to a midpoint temperature of the temperature measurements over the prescribed time interval. Based on the comparing, the system provides providing a compensated measurement for resistivity or conductivity of the water source. As a result, the system can calibrate the sensor continually during use, in real time, resulting in highly improved accuracy.