Vet at FirstVet answers:
A rabbit’s normal daily water intake is ca 50 to 150ml per kilo per dag. This means that a 2kg rabbit can drink up to 300ml of water a day. Rabbits that mainly eat a lot of fresh greens will drink less than 150ml/kg per day.
If your rabbit is drinking more than 150ml water/kg/day it is polydipsic, i.e. is drinking too much. You should book an appointment with a veterinarian if this is the case since polydipsia is linked to several different diseases and can be associated with pain.