Thanks to the many who responded to my original question several weeks
ago regarding ferret water bowls.
 
To summarize: I had two fairly new Oasis 1/2 gallon water bottles which
spontaneously decided to start rusting.  (Sidenote... Oasis has been very
responsive to this via email and has told me that they plan on
reevaluating the use of a metal cap on the bottle.) I was searching for a
way to provide my ferrets with a water bowl that they couldn't tip over or
otherwise foul up.
 
Almost everyone suggested a bowl that would attach to the side of the
cage, which I too had also thought about.  The other concern was that,
since the water was located next to their food, they would often drop
food kibble into the water bowl.
 
Ultimately I had to settle for a non-ideal solution, but the ferrets seem
to like it well enough.  I bought a couple of bowls whose base attaches
to the cage, and the bowl itself latches into that.  So they ferrets
can't tip it over and it's very easy to remove the bowls for cleaning and
refilling.  The base actually raises the bowl slightly above the level of
the food bowl so kibble-in-the-water is a rare occurrence.  I also bought
a small water bottle which I've set up alongside the water bowl -- in
case they drink all the water from the bowls they'll still have somewhere
to go.
 
So thanks to everyone who helped.  My ferrets now drink at least 3x what
they were drinking before.  It's a minor hassle to clean/refill the bowls
every day but if it makes 'em happy, so be it.  :)
[Posted in FML issue 3628]