personally i'm taking a 3l camelback and a US 1 quart canteen, plus a spare canteen for handling dirty water (as in river/spring water before purification)
If you need to catch/hold your source-water prior to filtration, you're better off with some sort of folding bucket or large thick plastic bag. I've rarely found myself in a position where I've needed to store/hold untreated water.
I use a Katadyn Hiker filtration unit drop the intake pipe in the river, connect the outlet pipe to an MSR or Ortlieb water bag. I then add steritabs to the bag, wait at least 30 mins and then the water is ready, it can be decanted into other bottles/water-packs as required.
If I'm in a clean (unpopulated) area with a relatively clean water supply, I have been known to just scoop up a mug of water from a fast-flowing stream and boil it. I would do exactly the same with rainwater (provided it was collected from a clean tarp).
But the 'system' of filter > bag > tablets is fool-proof and tried and tested.