Cooling and heating the environments in which we live or work is a common need in most inhabited areas. In Europe, the energy consumed for air conditioning is already on the rise, but the rise in temperatures in different regions of the world suggests a possible worsening of this need. To satisfy the need for cooling of buildings during the summer season, the most widespread domestic and industrial technology is the classic air conditioner, which often uses refrigerants with a high environmental impact and also requires a high electricity requirement. How can we reduce the energy impact of building cooling? A proposal comes from a group of scholars from the Polytechnic of Turin (SMaLL) and the National Institute of Metrological Research (INRiM), which has studied a device capable of generating a cooling effect without the use of electricity, the subject of research published in the journal Science Advances *. As in traditional devices, this new technology also decreases the temperature of an environment by exploiting the evaporation of a liquid. However, the key to the new solution proposed by the Turin researchers is to use simple water and common salt instead of chemicals that are potentially harmful to the environment. The environmental impact of the new device is also reduced because it is based on passive phenomena, i.e. spontaneous processes such as capillarity or evaporation, instead of on pumps and compressors that require energy and maintenance.