The goal we discussed after my ileostomy surgery was around 70 oz per day - preferably at least half being with electrolyes. (Given I am also limiting the amount I drink at meals to help with consistency of the output + not drinking for about 2 hours before bedtime to cut down on overnight bathroom trips, I would find it difficult to drink a lot more.)

The other thing I hear from all (including stoma, urology for kidney stones, and PCP) is that the best indicator of whether you are drinking the right amount is the color of your urine. It generally should be a light yellow. Darker means you are not drinking enough and clear suggests you are overdoing it.

Of course the corrolary is that whenever you go out it is a good idea to know where the nearest bathrooms are!