During post op, all liquids counted as liquid. So, even my protein shakes were also counted towards my fluids. I made sure everything I drank had protein except plain water.
Once I went on to actual foods it got harder but I worked out a plan that worked for me, but it was non stop drinking and eating, at least it felt that way. haha
I woke up, drank 8 oz milk (protein and fluids) then a bottle of water, then ate something, then a bottle of water, then ate something, then a protein drink (gatorade zero with protein was my go to) then another water.
It is easier now, but at first it was a chore.
I am still/always allowed to count my shakes towards my fluids but I don't anymore and still drink at least 80 oz a day and of usually just plain water. I LOVE and have always been a HUGE water drinker so it is easy for me. I can also drink "normal" now. Some people struggle so you just have to find what works for you.
You got this!