I recently switched Meeko's food from Canidae to Wellness Core, which caused him to drink more water. I have a waterer that holds 2 quarts (8 cups) of water. When he was eating Canidae 2 quarts lasted me a week, so a little over a cup a day. Now, on Wellness Core, 2 quarts lasts 6 days, which is about 1 1/3 cups of water a day. I should add that Meeko is a teapot, weighing in at about 10 lbs. If your baby is smaller than he won't drink that much.
I would measure out a 1/2 cup of water in the morning and see if he finishes it by bedtime. If he doesn't than measure whats left. If he finishes it, I'd add 1/4 cup at a time for the rest of the night. Do this for about a week and see how much he's drinking. This way you and your vet can discuss if he's getting the right amount.
It may also depend on what kind of food he's on and how much he's eating. If you're feeding him dry kibble, than he would be drinking more than if he was on a homecooked or raw diet. This is because kibble is dehydrated, all the moisture is sucked out of the food, during processing. So, he's drinking more as he eats to make up for that. Where as a homecooked diet isn't dehydrated and he'd be getting water from his meals. Another thing that would add to the amout of water he's drinking is how active he is. If he's a puppy and very active, he'd drink more. That's why I suggest measuring his water for a week. Some days he may play more and drink more water. When my boyfriend is around, Meeko knows that means tons of play time, and I know that means he'll be at the waterer at the end of their play session.
Good luck!
I remember you posted last month about going back to work and worrying about your Louie. Just wondering how he's doing while your gone? I'd love to see a picture of the little guy!
Oh I should add that Meeko doesn't drink or eat when I'm gone at school. He has bad separation anxiety and just lays by the crate door till I come home. So Louie might be the same, a little sad that you're gone and doesn't wanna drink?