The presence of leachable alkali ions, or their hydrated sites in the glass, is believed to be a determining factor for the interfacial water structure at the glass surface, influencing the surface properties of glass. The interfacial water structure on soda-lime silicate glass in humid ambience at room temperature was analyzed with sum-frequency-generation (SFG) vibration spectroscopy, which can probe the interfacial water layer without spectral interferences from the gas phase water. The soda-lime glass surface exposed to water vapor shows three sharp SFG peaks at 3200, 3430, and 3670cm1 in SFG, which is drastically different from the SFG spectra of the water layers on the fused quartz glass surface and the liquid water/air interface. The sharp peak at 3200cm1 is believed to be associated with the hydronium ions in the Na+-leached silicate glass surface. The 3200cm1 peak intensity varies with the relative humidity, indicating its equilibrium with the gas phase water. It is proposed that the hydronium ions in the Na+-leached sites produce compressive stress in the silicate glass surface; thus the growth of hydronium ions with increasing humidity might be responsible for the increased wear resistance of soda-lime glass surfaces in near-saturation humidity conditions.