Sprinkling water over the garden and the streets around the house is a traditional Japanese method of preventing dust on the road or ground from being stirred up and to invite cool air in the summer time. Sprinkled water evaporates and removes heat from the ground, which slightly reduces the temperature.
The way to sprinkle water is important. The optimal time for sprinkling water is generally around sunset and sunrise. Sprinkling water over the asphalt during the period when the temperature is high in the summer does not have much of a cooling effect because the water evaporates so fast. It is more effective to sprinkle water during the time when the temperature is relatively lower in the morning and the evening.
Sprinkling water in large quantities by hose and other equipment is not favorable. One tip for sprinkling water effectively is to pour it little by little on the ground or the wall of the house during the cool parts of the day.
Taken from vol.31 PDF