The Sawyer Squeeze Water Filtration System seems all the rage. My old filter died on the last Peaks walk I did. So I got Philip to get me a Sawyer Squeeze to pick up when I arrived in the US.
It has a hollow fibre filter which is rated to 0.1 microns - the rating you want to remove the bacteria and nasty stuff. It's supposed to last for a million gallons. But somehow I doubt it will be going for that amount of use.
This filter is fast to use (about 2 minutes a litre). Fill up the varied size bags that come with it and squeeze clean water out the other end. With a fast flow rate you can drink straight out of the nozzle. I did this a lot.
This is where it shines for me. In reflection, a soda bottle with it screwed onto the top, then filling up as you go past water and drinking straight through the filter is the way to go. Saving time as you walk. One thing: if you store it in your rucksack, squeeze air through it, flushing the water out - saving it from seeping out into your rucksack.
It can be back-flushed with the large syringe provided (but who is going to take that?) to clean it. Cost wise it was not a lot at around £30. It's light also.
BUT a caution. I used it a lot. Still, I got a water-borne infection. All the best kit won't stop that if you're not careful. Maybe some water ran down onto the nozzle or something. But I got ill. So maybe add a purification tab in to be sure in places like the US. But the main thing is be careful to stop cross contamination.
Either way, it's affordable, performs well and the flow rate is fast. The bags that come are rubbish long term. Use a platy or soda bottle. Make sure you keep unfiltered water from entering your clean water and it is going to be a good investment.