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Dehydration experiments on basaltic, andesitic and dacitic glasses with 1.1, 0.7 and 1.0 wt.% total water, respectively, were performed at 400–675 °C and 0.1 MPa. The dehydration rates were measured by in situ infrared (IR) spectroscopy and modeled by assuming the diffusion of one component water (total water). The diffusivities of total water in basalt and dacite were found to be linearly dependent on total water contents, but that in andesite was weakly dependent on or independent of total water contents at water content and temperature ranges of this study. The total water diffusivities in basalt and dacite were determined by assuming the linear-dependent diffusivity on total water contents and that in andesite was obtained by assuming the constant diffusivity. The obtained diffusivities of total water D (μm²/s) can be expressed by the following equations:where C is the total water contents in weight percent; C₀ …