I backpack a lot to in my home state of Arizona. It's dry here and even in the mountains water can often only be found in small pools below a rocky, bouldery stream bed surface. I use a MSR Sweetwater pump-type filter in these situations because it is easy to lower the water pickup into a pool well below its guardian rocks even though I can't get my hand in there. I use chlorine dioxide tabs as a backup and to neutralize the off flavor of stagnant water. When in wetter mountains, such as the Sierra, I use a Sawyer Squeeze or a Steripen (for short trips) and ClO2 as backup.