On my previous RV I had the faucets rigged with adapters so I could hook a hose to them. We used it for an outside shower but it could have been used for anything else like dousing a campfire.
Regarding using dirt vs water, there are places where campfires have to be out and cold to the touch with no embers remaining. The only sure way to do that is with water.
Looks to me that the OP is definitely talking about using his fresh water supply for fire duty. It's not a bad idea actually to have that hose on stand by in case a fire gets out of hand. In some boondocking areas any help may be a long ways off and your first line of defense is what you have with you. If you deplete your water in an emergency, so be it.
