I drink approx 2 - 2.5 liters a day (65-85 oz of coffee, water, soda, fruit juice, ...). Being active, part of it goes away when you breethe and through your skin (between, 0.5 to 1 liter).
This mean in 24 hours, I pee between 1.5 and 2 liters (up to 65 oz)...
I usually do my #2 30-60 minutes after waking up. I don't do it my diaper. It's the right time to put a fresh diaper. Depending on the day, temperature, how much I drink, I can keep the same diaper until my shower around 9-10 PM and put a fresh one for the night. Sometimes (or if I go outside in the evening) I change in the afternoon around 5-6 PM...
Answer: 2-3 a day my normal diaper is a Tena Maxi (european). It can swallow 1 liter without any leak, even seated on a chair the entire day.
I tried also with massive absorption ABDL ones. It's near the same. Well say 2 a day, at least to be fresh before going to bed and after #2!
Only if I go to a party and drink a LOT (not only alcohool, also water !), I might need an additional one but in this case I usually wear an Tena Ultima or an ABDL one.
Drinking more than 3 liters a day is not healthy (except in very hot/dry climate). You lose too much minerals. I this case, drink mineral water to avoid issues...