My little guy drank a similar amount at that age. He'd finish 3 or 4 400ml bottles of water over the course of a day and then 750mls over night (imagine that in nappies lol). That is in addition to any milk or tea he had. He still drinks a lot at 3.5 but not quite as much as he used to. I have water with me at all times. I was initially worried and spoke to my GP about it, but she wasn't worried.