Report in the Veterinary Record, Feb 19. 2011
Vets at the University of Zurich have looked at dwarf rabbits and how they prefer to drink. They showed a clear preference to drink from open dishes rather than the commonly used nipple drinkers, and in particular any rabbits which may be 'compromised' by urinary disease should have water provided this way. Interestingly even rabbits which were used to nipple drinkers preferred the dishes.
Even short term water depravation reduced food intake, so the impact of rabbits not drinking optimally is of potentially great importance.