The water temperature in open reservoirs in summer is always lower than the ambient temperature. Why?

Because in summer, water evaporates more intensively, and the larger the area of the open surface of the water, the faster the evaporation. When water evaporates, it loses energy, so its temperature drops. In addition, the heat capacity of water is much higher than that of the surrounding air. Those. more energy is required to heat a unit of mass of water than a unit of mass of air. Also, the surface of the reservoir acts as a mirror and reflects part of the sun’s rays, but the air does not. The cumulative effect of these factors leads to the fact that in summer the water is colder than air.