Giving 9 month old water

So my baby is overweight according to her pediatrician he says instead of giving her formula when she wakes up in the middle of the night to just give her water. I’m not sure how I feel about that because I thought and everyone I know says babies should be drinking a lot of water.. opinions??

Update- thank y’all!! I don’t think I want to be seeing him anymore. She’s a little over 2ft in height and she weighs 25 pounds (he says she should be weighing 18 ibs) .. I do think she’s chunky (the best kind of babies) but not overweight and obese.. she’s standing up on her own and walking along side furniture and he told me months ago she’d be too heavy to walk but she’s doing just fine :)