How many ounces of fluid is your 3-4 year old drinking?

So my son is developmentally delayed and non verbal (less than 10 words). Well the past 2 weeks he’s been extremely picky with eating and drinking anything, and the last day or so he will say “ow, peepee” and point to it and so I’ll put him on his potty and he just dribbles. I’m thinking he’s not getting enough fluid due to him fighting us with every thing we offer him. He is not showing signs of dehydration or anything but I’m kind of stuck. Covid and dr appts are next to impossible right now.