@SquidPresident hey, the fact that you know you don't know and are willing to admit that and look for the answer puts you head and shoulders above people who just trust whatever grandma did

(but i actually know the answer to this for some reason - if the kiddo is still on bottles, only formula/breastmilk, that's hydration and also needed calories. stepping up to other liquids is a developmental milestone that can be ok'd when you get there, typically when baby is on baby food for calories.)