What everybody else said. I have three steel bikes that sat on a patio two blocks from the Pacific Ocean for about two years, salty mist on them nearly every day, and while they did develop some superficial rust, nothing significant happened (they'd been Frame Savered, which probably helped). My racks, a Thule and a Yakima, got light rust on some of the fasteners and rivets, but that's all. I'd rather there were no rust at all, but indoor storage wasn't possible.
Coating exposed parts with wax or clear nail polish might have helped. Fresh water, from rain or stream crossings, shouldn't be a problem. My mountain bike has been completely submerged three or four times without damage.