I'm leaning toward what Al says. Not to sound preachy, but has your friend had a recent physical and specifically done a parasite evaluation? A quick scan through non-peer reviewed internet discussions suggests the _possibility_ of neurological issues or possibly anemia from long-term exposure. But more relevant, there were several discussions that Aquamira may not be particularly effective on Cryptosporidium (note his complaint of digestive disorders) and/or that the exposure time was long (some claimed up to 4 hours). More telling was the company's own report using an animal model of effectiveness (neo-natal mice infected with Cryptosporidium or Giardia then treated, mice sacrificed then diagnosed for spores). If I'm reading the report correctly they had 100% effectiveness at 25 C. BUT they had 0% at 4C.
And even if 100% effective under normal conditions, using it for 6 months straight would likely present the possibility of occasional under-treatment, or missing a treatment completely (note that one of the selling points is that it doesn't flavor the water...I could see after a long day of hiking sitting down to treating your water, getting distracted with something else, and forgetting you didn't treat it since there is no change in flavor and drinking it). You'll also note that Aquamira, in addition to selling chemical treatments, also sells filters. The filter descriptions SPECIFICALLY list that they filter out Crypto and Giardia. Those claims are noticeably absent from their chemical treatments.
Jeff
