Uchimizu refers to the action of sprinkling water on the streets in the summer and has been a tradition in Japan for many many moons. The water keeps the dust low and cools off the immediate area. You can read up more on this tradition somewhere here.
The Uchimizukko Daishugo event has made this tradition more interesting by getting legions of maids to do the watering. Video included after the jump.
The pink maid in this pic wearing glasses was my fave out of the lot.
BTW, just added this image to the Wallpaper pool.
