Porous glass tiles have been reacted with a low-surface energy coating to produce hydrophobic surfaces. Washing the surface with surfactant reduces hydrophobicity and the wetting state changes from Cassie-Baxter to Wenzel. Passing air through the porous glass when it is immersed in water causes a solid-gas-liquid interface to form and this is associated with recovery of hydrophobicity. The processing and microstructural characteristics of the porous glass that show this effect are reported. Potential applications include low-friction pipes, where maintaining the Cassie-Baxter state at the water-pipe interface would significantly reduce the energy required to transport water.