Other mistake: After the apartment house fire, the restored old engine is trashed by a hail of bricks. Later, when Roy and Johnny are talking about who won the first prize, The Old Engine in the back looks nothing like it did when it was wrecked on the street. Also, the shot of The Old Engine that's shown here, is actually the same footage shown in season 3, "The Old Engine", with the lighting dimmed to signify nighttime, when at the end of the episode Roy and Johnny decide to keep it. Note the exact same broken pieces of windshield, tires, hubcaps, dirt, shadows, everything.
Other mistake: When Johnny and Roy leave for the parade, they turn to their left when leaving the fire station. When Station 51 is toned out to the structure fire, where John and Roy are, they turn to their right when leaving the station.
Answer: It is standard practice to wet down driveways so that they stand out in a long shot.
stiiggy