Can try procati sweat less sugar add with some water. This is told by doc that I can give him. Especially when he is sick he don't drink milk or water. Now he recover I still continue to let him drink. As sometimes he doesn't wan to drink water. Or baby juice I will also add water so that it won't be too sweet.
https://ph.theasianparent.com/get-your-child-to-drink-more-water
depends on age
Cup?