<p>This paper is about various physical properties of water that are significant for the local climatic conditions in urban areas. Based on the water and energy balance, selected terms are quantitatively discussed in terms of their impact on the urban environment. Furthermore, the extent to which the enthalpy of evaporation can contribute to cooling not only surfaces but also the near-surface atmosphere on warm or hot days is demonstrated. Using examples of the transpiration efficiency of different tree species, it is shown how vegetation can create these cooling mechanisms during warm summer days. There are different options, how cities with a high proportion of water surfaces relative to their total area (water towns) can mitigate high surface and air temperatures by water surfaces.</p>