Is it normal for my cat to be drinking more, now that we switched him to dry food?

He used to eat canned wet wellness cat food, but recently (few months ago) my vet had us switch him to a dry brand (Royal Canin Hypoallergenic) for his skin. I noticed he's been drinking a LOT more water lately though. Like he never drank it before, and now he drinks at least a bowl of it a day. Could it just be because he's not eating wet food anymore (so he need moisture differently), or could it be something else like feline diabetes? Also, he was originally 18 lbs. but now he's about 15 (he lost it within a one year interim).