To add to an old discussion, I just bought a Grayl Ultralight for 3 week overseas trip that would help make municipal water taste better as well as supply water from streams during day-long hikes. Their 2016 model weighs less than the original version.

It worked really well, and I would recommend it to others. I was able to refill other people's water bottles with (filtered) sources, and that made me some friends! Capacity was appropriate, easy to use, and although an expensive initial purchase it will probably pay for itself in 6 trips because we aren't buying bottled water. Plus the assurance we would have access to drinking water no matter the suspicious source was worth $ to me.