[cypher]

That is a lot of water & it's unusual for them to drink that much if they're healthy, he should be peeing more too if he is drinking that much, have you checked around the cage to see if he's peeing somewhere he doesn't normally.
If he seems fine in himself then you could just keep an eye on him for a few more days & see how he goes but it is a bit of a concern, there are various things that can make them drink more but without any other symptoms it's hard to guess, if it continues it might well be worth having your vet check him out.