STOP and let the cows teach them to drink. Calves are just going to be relying on their mommas for their liquids for the first few weeks, then they'll start drinking water on their own once they're inquisitive enough and want to taste and try everything that their dams are eating and drinking. The calves' dams are the better teachers than you can be, so I would stop interfering and let the cows do what they do best.
You're not bottle feeding them, obviously, so just let them be. Let the cows do the teaching.