To know if whatever you're doing to your water really works, you'd have to send samples of both untreated and treated water from a number of sources to a reputable lab for testing. I wonder if anyone has done this? In fact, I wonder if the manufacturers have done this, because I sure haven't found any evidence on their websites that I've looked at.
That being said, I filter my water regardless of source. Some years back, I had a friend get a really nasty case of giardia from a spring in the high Cascades. That was the only place on the trip that he didn't filter his water, because it was coming right out of the hillside.
Most of the manufacturers link to studies done, and most of the studies are reputable (a counter-example was the "LifeStraw" that popped up and was clearly crap with crap studies.)
They've got the best testing that I've seen. They do more along the lines of EPA testing with real pathogenic organisms.
Potable Aqua has NOTHING, Aqua Mira has ... a ... less than ideal test done by Dr. Ryan Jordan (sound familiar?) proving it kills biofilms, his speciality, but nothing else. I'm not doubting the product efficiency, presumably some other research exists proving chlorine dioxide kills, but here's the 'study'.http://www.aquamira.com/consumer/aquamira-water-treatment-drops/BPL_2_Efficacy-of-Water.pdf
I'm not even going to go into the filters, etc.
It's easy to test any water purification product in a lab. You lace the water with, ideally, an extremely hardy organism such as certain viruses or spores. You treat the water with product, then pour water onto agar plates (which grow bacteria very well), and see if anything grows. Sterility controls and control samples, etc, are all very important, but that's the basic procedure.
Now, I haven't completely thought this through, but you should be able to test things at home by doing this:
Get two jars half-full of water, dump a bunch of sugar, maybe a bit of starch in, and then seal up one... drop your chlorine tablet in the other one, seal it up, and see which one molds over first <img src="/forums/images/graemlins/grin.gif" alt="" /> Variations of this can be performed with other products, with contamination from the air and yourself a huge issue however.
OregonMouse, I made a huge big post in the other forum about giardia and the wild. The general idea is that no, it's not a problem (in North America mountains), and that if your friend caught giardia from a mountain spring, he or she was almost certainly infected by human hygiene issues related to that spring and/or other hikers (ie pollution or cross-contamination).
No manufacturers actually go out and TEST wild water, because most mountain streams in North America are clean. It's not very convincing to publish tests stating your product isn't necessary. There are a few researchers who do it themselves, and the general result from the Sierra is very clean water. (check that other thread for actual links). Beaver Fever should be called Human Fever - beavers catch it from humans!