My experience is that if your rabbit is eating green leafy vegetables, it is possible for them to get all the water they need from the veggies. Bunny poops are very dry, and they will excrete only tiny bits of water in their poops. My experience with my last bunny was that with an all diet of green leafy vegetables, she wouldn't drink water at all.
Unfortunately, my current Flemmish baby girls don't provide much help for a basis of advice about eating and drinking. They eat copious veggies, pellets, fruit treats, cardboard boxes, paper bags, wood chewies, etc. and drink water....every thing just goes down the hatch. They are are growing!
In many ways, rabbits are very robust and hardy. However, with personal, very sad, experience with rabbit eating, is that they are also very fragile, and I'd guess that also with drinking water ...they can be fragile also.(?) I'd say take your bunny to the vet and have a blood test. This will quickly tell if bunny is dehydrated.
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Even here is the Los Angeles metropolitan area, there are relatively few rabbit vets. My experience is that you should establish a rappoire with two rabbit vets. When bunny gets sick, you don't want to have the problem where your bunny doctor is unavailable...have a back-up doctor. If your rabbit has not eaten for 12 hours (18 hours?), it's a medical emergency and you need to see a rabbit vet...and if your vet is not available, you need a second vet to call.
