Thanks for all the responses. Sounds like we should try and filter from side streams if possible. I'll look for a list of good places for water.
The Jerrycan looks cool, but this is a kayak self support trip; so no space
For coagulation and flocculation agent I am trying out the GCPBA water wizard for river runners; I work in water/waste water industry and couldn't resist trying PACL.
I really like the idea of taking lemons and some powder to supplement. Will be great in cocktails too!