Modulation excitation diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) together with resistance measurements has been carried out to study water isotopic exchange on undoped SnO2 materials as a function of CO concentration. We compare two materials synthesized via hydrothermal treatment and different only in their precursors: SnO2 Ac synthesized from tin(IV) hydroxide acetate and SnO2 Cl from tin(IV) chloride pentahydrate. DRIFTS and resistance measurements were performed simultaneously in an environmental chamber at 300 °C and in a flow of humid air. The annealed materials were found to have similar particle sizes (16±7 nm), crystallite sizes (12±2 nm) and pore size distribution (9±1 nm). However, sensor tests showed notably higher responses to CO in the presence of water vapor for SnO2 Ac. Electronic effect of CO chemisorption quantitatively correlates with consumption of bridging hydroxyls on the latter surface upon increasing concentration of CO from 0 to 500 ppm in humid air. No such correlation was found for SnO2 Cl. Water desorption kinetics was found to be slower for the latter by ca. 30 % with respect to SnO2 Ac. Low activity of surface OH groups and consequently low sensor signals of SnO2 Cl were proposed to originate from traces of Cl ions found in the material after the synthesis despite negative Cl test before the hydrothermal treatment.