We hiked about 4.5 miles yesterday. When we left the trail my 3L Camelbak had about 8oz water remaining. In retrospect there is a functional challenge with hydration systems and that is not knowing how much is left and what your consumption rate might be. Clearly the 3L required trail discipline.... The weather yesterday was in the 70s (F) and overcast. If the trail had been wet and rainy then I could make drinking water everywhere but in this current climate the trails were dry and the best water sources could be an hour off trail.
Before we started the hike we decided to stop when we reached water or our time-limit. When got to the portion of the trail that was under water we turned around. Since we were both carrying Camelbaks we thought we had enough water.