I use the same metal waterers, and prefer the 3 gallon size. The two gallon size would work for a few birds too. The five gallon size is heavy and awkward, and if carried by that small handle on top, the handle will fail.
I take mine outside to fill, and replace the top sleeve outside, so there's no real spillage inside.
Here we have an all weather hydrant next to the coop, and GFI outlets inside the coop.
For years we ran a surface outdoor rated electric cable to the coop, in conduit, and it worked well. Not to code, and finally all fixed up to code a few years ago. It actually wasn't all that expensive...
Mary