That doesn't work in many places. I couldn't tell you how many ponds and springs I've seen on topo maps that are dry when I got there. Good way to really be screwed a long way from the truck. If you're in an area where the springs and ponds are really reliable, then yea, maybe so.
4 liters of water is nearly 9 lbs. Add that to a pack for multi-day trips that's already 30 lbs. and it makes up 25% of the pack weight.
I once did 52 miles in the Guadalupe Mts. of W. Tex, carrying all my water the whole way. Started out with a 5 gallon collapsable container in my pack that weighed 60 lbs. total. But I was younger then. LOL
I'm trying to find ways to cut weight and water seems to be an obvious place. My purifier weighs nearly a pound, and I've been looking at lighter options there but just haven't pulled the trigger on one yet.
I did 8 miles yesterday on 1 L of water. For whatever reason, I don't drink as much as most folks do. Maybe because I don't sweat that much? I'm going to start packing 2 L / day and 1L for day trips and see where that gets me.