I agree that it is VERY confusing. Even when there are resources out there that are supposed to help clarify things, even those seem to be confusing. For example there is a site out there that is some kind of independent Army comparison of water cleaning systems. They rate some stuff good and other stuff bad based not upon their studies (as something like Consumer Reports would do), but based upon reading other peoples' studies whose controls/techniques are essentially unknown.

From what I can tell the two real nasties are giardia (as you mention) and cryptosporidium, both of which come from critters' (human and others) fecal matter getting into the water sources.

Both are protozoa - one celled critters. As I understand, the adult critters can be filtered from water, but they produce oocysts (like an egg or spore) that are only filtered out by very very fine filters. These are supposedly very resistant to chemicals such as iodine and chlorine. In relative terms, crypto is MUCH more resistant than giardia. They are so resistant to filtering and chemicals most say the only real way to be sure to remove risk is by boiling water.

I suppose there are some ultra-fine filters out there that can remove even the crypto oocysts, but I would think these would plug up very fast.

Though even chlorine doesn't kill giardia & crypto, they say chlorine dioxide (micropur tablets) will kill the oocysts, but only if enough contact time is allowed. The problem is that water temperature has a lot to do with that contact time, so colder water takes longer (up to 4 hours for crypto & 30 mintues for giardia) than warmer water.

The other little battle out there is whether the MIOX "mixed-oxidant" solution sufficiently kills crypto. I'm not sure how it compares to Micropur tablets. Clearly this stuff is much better than chlorine. The suggestion is that they are about the same, but nothing I've read clarifies this for me.

So, that gets me to wondering how much of a problem these nasties are out in the waters people might be trying to drink from. I haven't found a good source with advice on how to know what the risks are. As far as I can tell the risk is always there - just about anywhere, but some areas are much worse than others.

BTW, based upon what I've read, I ended up buying a MIOX and four 4L (1 gallon) Platypus water tanks for my BOB. The MIOX can easily treat many liters at a time. This should allow me to keep enough water in treatment for my family. If the water is really yucky (lots of suspended particulates) I can try to filter it first using a bandanna, clothing, or whatever. I do not EDC water treatment.