We have measured with use of a surface forces apparatus the short-range forces between two bilayers for a series of zwitterionic amphiphiles with different headgroup sizes and dipole moments. We found that the compression of two bilayers is discontinuous, revealing 1–3 steps of 0.27 ± 0.05 nm. This corresponds to the characteristic size of water molecules squeezed out layer by layer, suggesting the structuring of water close to the bilayers. Other possibilities are discussed.