Other mistake: At the start of this episode the tones drop and Station 51 is dispatched to a fire and explosion. In this closeup, all the guys come running from the kitchen into the apparatus bay and head for the vehicles, but wait, none of them are actually 51's guys.
Other mistake: When Roy and Johnny are with the guy who somersaulted off the roof into the pool, Johnny is in the pool giving him oxygen, and in the closeups Johnny's left hand varies between very hairy, not hairy at all, normal fingernails and bitten up fingernails. Additionally, the hand holding the mask on the boy's face changes back and forth between Johnny's left and right hand, between shots.
Answer: It is standard practice to wet down driveways so that they stand out in a long shot.
stiiggy