A surface (30) suitable for promoting the formation of droplets 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 vapor comprising passing a vapor across such a surface (30) and a method of purifying a liquid by passing a vapor containing droplets of a liquid over such a surface.