Water is your life-line on the trail. It will keep you going, even if you have no food to eat. That is why I plan a half-way stop for each leg of my route, that falls exactly on a body of water. No doubt, you are going to need to refill your canteens at some point through out the day. Packing enough water for an entire day will seriously weigh you down.
Depending on the season, I have gone through anywhere from 3 to 8 litres of water during a day of hiking. Each litre of water weighs 1 kg, so for weight I am looking at almost 20 pounds of water for a hot summer day! Having said that, I don't hydrate my body days before a bug-out (like a marathon runner would), so I always end up sucking water like a sump pump. But then again, if it is an emergency bug-out, you wouldn't hydrate your body beforehand either, so I think my water numbers are pretty reasonable.
My point is, pack 3 to 5 litres of water in your bug-out bag, and fill them up at the half-way point. That will cut your weight in half for the first part of the day. If its summer, pack 5 litres. Fall and spring, you can get away with 3. Winter...well we'll talk about winter later.
Soldier, out.
