Hello there!
My little Wicket spits up sometimes after drinking lots of water...particularly if I pick him up shortly after he just drank a lot! It's always clear and looks pretty much just like water...I've never worried too much about it. He always just goes back to playing and being normal, so I figure it's nothing to be too concerned about. We go to the vet on Saturday so I'll just mention it to her and let you know what she says (if you're interested).