13 month old refuses water

So up until about a month or two ago he loved water sippy and no problem if I watered down his milk but now he will not touch water and spits out his milk if I water it down at all ... I know he’s not supposed to have milk for every bottle of the day and now he’s to the point where he drinks half a gallon every day and it would be nice to just use water when we go places so it’s not a big deal if we run out of milk. Idk what to do 🤦🏼‍♀️🙇🏼‍♀️🤷🏼‍♀️

He’s also over 30 pounds 😩😅