Hoses and such that are attached to a water line should have a vacuum (anti-siphon) breaker. This prevents water from back-flowing into the fresh water supply in the event that water pressure drops. It does this by allowing air into the water line, in this case, the shower hose, so it can't suck in dirty water.
Most of the parks I've been to have an anti-siphon on the spigot anyway. But it's still a good thing to have because even a small amount of dirty water can contaminate the water in your fresh water supply lines and make you sick.
If it were me, I'd remove the breaker, attach the hose, take a shower then go to the hardware store to get a replacement.