Just a recent experience to show what can be done (this in no way says this should be attempted!). I did a 100 mile ride last week with 2 20oz bottles of water, one with carb mix the other with electrolyte tablet. I was in a good groove and didn’t feel the need to make any water stops over the 5.5hr or so duration and I rode a steady pace (66%). I also consumed 1000 calories (ride itself was 3600kj of work), so probably less than is advisable for others but works for me