In reply to waterfall:
Another vote for the Sawyer mini - I've used mine inline with a bladder (make sure it's round the right way). If you want to fill from streams, it comes with a soft bottle to screw onto and will screw onto many others.
I've also got a Water to Go bottle - LifeStraw is similar, but I've not used any of their options.
The nice thing about these ones is you can fill and drink almost instantly, but be careful with filters in very cold conditions - if they freeze, the filter could crack and fail.
UV is good, but needs a couple of minutes to work and you might need to pre-filter the water to make it clear enough for UV to work effectively and the batteries can run out.
I assume you're not going anywhere coastal, where desalination would be an issue?