Florida gets ALOT of winter visitors. You might want to re-think not making reservations - especially if you're planning on doing Disney. Ft Wilderness sites are in high-demand during Feb.
The farther north you plan on staying, the more likely you are to get sites. But also more likely to be cold.
Monkey44 mentioned that Flamingo has water/electric sites, but unless there has been a change since last year, the sites do have electric but not water.
Water is available from a communial spigot near the showerhouse. Reservations there are not site-specific, so you can't go on line and just choose a site near the water source.
Just our experience. YMMV.
G-half can always find a way to do things upside-down, inside-out or backward.
It's his Super Power!