Trivia: At the start of this episode, Station 51 and other FD companies are at the training center, to find the best way to deal with sulfur trioxide. Notice the tanker in the background, which contains the sulfur trioxide, particularly after 18's guy falls into the trench, when they all work on helping him. It should look familiar. It's this setting that was used in the newer Emergency! intro that is shown at the start of each episode, where we see Roy and John in turnouts, treating the man dressed in blue who's lying on the ground between them. The specific rescue we see in the intro is not actually from any of the episodes.
Trivia: After John and Roy dial the wrong number twice, it cuts to a shot of LACoFD headquarters, and the dispatcher, Sam Lanier, transmitting the paging tones. In the closeup of the Motorola Quik-Call, note the company numbers on the tabs and that all FD companies are in numerical order except for 51, which is placed beside 127. (Can also be seen in other episodes).
Answer: It is standard practice to wet down driveways so that they stand out in a long shot.
stiiggy