Mono-molecular layers, or monolayers, on the surface of water can reduce evaporation by up to 40% on small storages. Effective reduction requires the maintenance of coverage by dispensers, which must be informed by sensors capable of detecting the presence/absence of the monolayer. However, no system has yet been developed that can reliably automatically detect the presence of monolayer. Numerous detection techniques for potential field deployment, including optical and infrared reflectance, measurement of surface tension and wave damping methods were investigated. A wind assisted surface probe (WASP), based on the temperature differential between the sub-surface and volume of a small sample of periodically-entrapped water was subsequently developed. In small scale testing it has shown to be a reliable indicator of monolayer in all but very high humidities.