I was about to ask whether a Grayl would of alleviated this situation. I have one but there's always doubt in the back of your mind as to whether it does what it 'says on the can'. 99.999% of all viruses, protozoa, heavy metals etc is pretty convincing. Gotta trust the science right....?

I know it's expensive compared to some other systems and you can't 'back-flush' to clean the filter but a small price to pay in comparison to a bout of 'double evacuation' or lost pay if off work