A surface (30) suitable for promoting the formation of liquid (35) is provided comprising alternating regions of liquid repelling (32) and liquid attracting (33) material in at least one direction across the surface wherein the diameter of the droplets is controlled by the size of the smallest dimension of the liquid attracting material. The surface (30) may be textured and/or form a pattern. Also disclosed are a method and a system of collecting a liquid (35) carried by or condensed out of a vapour comprising passing a vapour across such a surface (30) and a method of purifying a liquid by passing a vapour containing droplets of a liquid over such a surface.