© 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. We revisit the main HI-to-stellar mass ratio (gas fraction) scaling relations, taking advantage of the H I spectral stacking technique to understand the dependence of gas content on the structural and star formation properties of nearby galaxies. This work uses a volume-limited, multiwavelength sample of ~25 000 galaxies, selected according to stellar mass (109 M⊙ ≤ M* ≤ 1011.5 M⊙) and redshift (0.02 ≤ z ≤ 0.05) from the Sloan Digital Sky Survey, and with HI data from the Arecibo Legacy Fast ALFA survey. We bin according to multiple parameters of galaxies spanning the full gas-poor to -rich regime in order to disentangle the dominance of different components and processes in influencing gas content. For the first time, we show that the scaling relations of gas fraction with stellar mass and stellar surface density are primarily driven by a combination of the underlying galaxy bimodality in specific star formation rate and the integrated Kennicutt-Schmidt law. Finally, we produce tentative evidence that the time-scales of HI depletion are dependent upon galaxy mass and structure, at fixed specific star formation rate.