As long as you take the puppy out to pee when needed so that the puppy won't be peeing in the house then it's okay to leave water out for the puppy and allow the puppy to drink as much water as they want to per day.
That's the best thing to do so that you make sure the puppy stays hydrated is to just keep a bowl of water out and allow the puppy to drink as much water as they want to drink throughout the day.
Just like you should drink as much water as you need too or allow your kids to drink as much water as they want too so that they stay hydrated.
I've always just left a bowl of water out throughout the day when I had a puppy and then let him drink the water as needed.
Then during the night an hour before bed I would put the water up for the night so the puppy wouldn't need to pee at night when he wasn't house trained.
After he was house trained to go outside to pee then I would let him drink water throughout the night as he needed too.