Only once have I got sick and been able to blame water was shallow turbulent warm water near the hump back bridge on the Orongaonga river. There was about 200 people picnicking upstream at the time. Never will know if it was the water but it passed very quickly in both senses of the description
:) been there, done that, not pleasant!
Camping at a well used horse camp (in Aus) and collected water from a trickle down hill - my filter broke so I had to just hope for the best. Started squirting 10 hrs later and took 2 days to process. Very low energy levels as well.
Once in x years of tramping (where x is a large number :) is pretty good.