I have switched to a water bladder system, actually a Platypus with a wide opening to put crushed ice while walking in the summer in California from using Nalgene bottles. They are more convenient while walking, with bottles either you have to have someone get the bottle from your side pockets in your backpack or taking the pack off your back.
I take a small Nalgene bottle if I bring some of the energy powders to add to the water. I have a small wide mouth, I think it is a 14 oz bottle that fits on a bike water bottle holder. I don't put anything in the Platypus besides water.
We are walking from Sarria to Santiago (not enough time) and by reading the posts, watching some trip videos and looking at the map, we may take a 2-Liter Platypus just because they are the smallest we have but we probably only going to fill it between 750 cc to 1L only.
We just did a 13 mile with the Boy Scouts, the weather was what we expect in the late April/early May, there were a lot of steep hills and muddy roads. I took the 2L Platypus and only used 1L of water during the hike plus about 12oz of the energy drink during the lunch break.