Revealing mistake: At the movie studio, when the actor who plays Dr. Ned is loaded onto the ambulance stretcher, their set's 'fake' window area is the same as Rampart's 'real' hallway later in the episode. We can see this when Brackett, Early and Dix walk down the hallway to kick Dr. Ned's film crew out of his room. Pretty funny to see the same chairs, wall, window with painted exterior backdrop and color stripes on the floor. This area of Rampart can also be seen in the previous episode 'Family Ties', when the clock radio shorts out causing a fire in the patient's room.
Answer: It is standard practice to wet down driveways so that they stand out in a long shot.
stiiggy