A METTLER TOLEDO water conductivity sensor can be calibrated against a solution of known conductivity (much like calibrating a pH sensor against a solution of a known pH). Alternatively, an in-line water conductivity sensor that contains a range of very precise resistors that duplicate known pure water conductivity measurements can be used.
For applications in the pharmaceutical industry, special considerations should be made for compliance purposes when calibrating a pure water conductivity sensor. The UniCond Calibrator and Pharma Waters Verifier can help ensure that your calibration is pharmacopeia compliant.