Certified GKH Gardening Expert
If you turn the hose off, nothing can come out, since it is off. It is not an outlet for your house water system, it is part of your water system. All water feeds from your water heater or ground supply and goes to all outlets in your home, including your hose.
Water from all sources in your house go down the drain to a single pipe which feeds to your septic, or sewer lines.