Nancy,
 
We've never had a problem converting any of ours or the shelter's.  If I'm
doubtful, I'll take them over to the bottle, put their mouth up against it
and squeeze the bottle enough that a couple of drops of water come out.  At
that point, they'll usually lick the water and find that water keeps coming
out as long as they lick.
 
Dick B.
[Posted in FML issue 1203]