Evaporative cooling is a remarkably efficient way of cooling down a space, commonly used in desert regions before the invention of air conditioning. The phase-change of the water from liquid to gas absorbed a lot of heat from the building. The gas was condensed outside the building, where it released its heat.
The hottest part of a building in my region is the roof. The bright sun shines upon it, and most roofs are, for reasons that escape me, dark in color and absorb quite a lot of heat. Instead, we make the roof transparent with white underneath, and between the two layers flow a layer of water. When the water reaches the gutter-area, it is siphoned off into a recycling area that condenses it and vents the heat into something else, like a swimming pool, hot tub, or a greenhouse. Air conditioning bills will be reduced, though unless the water is carefully recycled, this would be harsh on the water bills.
A slightly less efficient version of this has a large, leaky hose on the topmost part of the roof, thereby making it rain perpetually at your house. Rain that absorbs 85% of the heat on your roof.