I hit a something in the backflow system with my car, and the pipe is leaking...?

Do you mean the backflow preventer for an irrigation system? We need more info.

Ok, if you have the main valve for the backflow shut off, it has no effect on your house water. The backflow is a safety device to prevent any of you irrigation water to siphon back into your house. Here's a scenario: Say there's a heavy thunderstorm and the ground is saturated. The power goes out. Someone in the house turns on a spigot. Without the backflow, it's possible to have the ground water siphon back into your potable water supply. Not a good thing, especially with insecticides, fertilizers, and herbicides that may be on the lawn. The backflow prevents this. But again, if you have the main valve for the irrigation shut off, you'll be fine until you cab get the backflow repaired.

possibly