NOVELTY - The strong acids content in sample water (1) is increased to increase equivalent conductivity of impurities, by utilizing cation exchange resin together with anion exchange resin. Cations and anions of sample water are respectively adsorbed on cation and anion exchange resins, to form strong acids. The increased conductivity of impurities are measured, and impurities in water are monitored.    USE - For monitoring impurities in water used such as cooling water used in industrial equipment, including thermoelectric power station, atomic power station and semiconductor manufacturing equipment.    ADVANTAGE - The method detects the inflow of impurities of low amount at high sensitivity. The measurement sensitivity is increased in the range of 40-200% by converting carbonate ions of low conductivity into chlorine or sulfate ions of increased conductivity, and the amount of the inflow of air or organic substances is measured by a simple and an efficient method. The conductivity of the impurities is measured in real-time, without heating.    DETAILED DESCRIPTION - The strong acids content in the sample water is increased to increase equivalent conductivity of the impurities, by utilizing a hydrogen-type cation exchange resin together with a chlorine-type anion exchange resin. Cations of the sample water are adsorbed on the cation exchange resin to form strong acids and the weakly acidic anions of low dissociation degree in the sample water are adsorbed on the anion exchange resin to form strong acids. The increased conductivity of the impurities are measured in real-time and impurities in water is monitored.    An INDEPENDENT CLAIM is also included for high-sensitivity apparatus for monitoring impurities.    DESCRIPTION OF DRAWING(S) - The figure shows schematically an apparatus for measuring cationic conductivity.    Sample water (1)    Valve (2)    Flow meter (3)    Cation exchange column (4)    Electrode (5)    Conductivity meter (6)    Anion exchange column (7)