Carbonic acid (H2CO3) has recently been identified as one of the contaminants contributing to stress corrosion cracking of low-pressure turbine disks in addition to being involved in low-pH erosion-corrosion of steam and return lines and corrosion in the air-cooling zone of watertube condensers. Many attempts to establish the exact amount of H2CO3 in these systems were not totally satisfactory because of a lack of a selective, accurate and sensitive technique to assess low microgram per litre levels. In this work, a new technique based on non-suppressed ion chromatography has been successfully applied for examining the H2CO3 distribution in samples collected at Hydro-Quebec's Gentilly 2 nuclear power plant and Ontario Hydro's Nanticoke fossil plant. Performed for two random conditions, the analyses revealed carbonic acid levels ranging from 5 to 74 μg/L with a specific distribution for each plant and a dependence of the relative volatility on the temperature, pressure and/or chemistry. Finally, the two Canadian plants investigated in the present study have shown comparable H2CO3 levels with a German PWR plant operating under an AVT control based on hydrazine addition.