Because Montag asks Faber to light the sprinklers in the garden?

I'm not sure exactly what you question is asking.... Montag asks Faber to turn on the sprinkers to remove his scent.... to make it harder for the Hound (or others) to track him.

Then, turn on your lawn sprinklers as high as they'll go and hose off the sidewalks. With any luck at all, we can kill the trail in here, anyway..'