I found out a long time ago that I just can't hang a water bottle properly! I bought a fancy new-fangled kind for Camden that just poured water out of it, so I went back to the old-fashioned style. But Bubba is in charge of water for the chin. Every time I fool with it we have water every where!
Birds are bad about pooping in their water, and when it's an African Gray the smell can run you out of the room! I had my first Gray trained to use a water bottle for a while, then being a Gray she started playing with it. The fun came when one day I had a glass bottle on her cage and she managed to knock it down onto the tile floor. No more glass bottles in this house!
I think it's a trial and error thing. Since your piggies are used to a
food bowl attached to the cage they may think that the water being there to is perfectly normal.
Like dealing with a bunch of 2-year-olds, isn't it?

How do our animals get to be so picky?