When I was at my last WDW trip (2 days ago), we were at MGM about 10 minutes until park close, and we were making our way along the Sreets to get to the exit. Along the way, we saw a fire hydrant near the "subway" entrance, and there were 2 little sprinkler type things spraying out of each side of the hydrant. They were moving the water from side to side (just like some sprinklers do) just spraying on the streets, and some of the sidewalks. Does anyone know what it's for, or why it does it?