This is a fascinating subject because it contains so many variables, the terrain, the altitude and weather, condition of hiker and most important the length of hike just to mention a few. But at 3 liters per day each for a four day hike would add, 12 liters or weigh 26 pounds. How about the food, and other essentials. U.S. Army uses 4500 calories a day as limiting. I think that comes to 2.76 mikes an hour for 8.5 hours
Many reach for distant shores only to run to the safest harbor.