There are no tests I'm aware of unless one has access to a lab. If someone could come up with a reliable, reasonably priced test, I bet they'd sell well. As it is, there are scores of people out there using filters that may or may not work. Good thing the waters in the wilds of N. America are actually pretty darn clean. I bet that if the waters were as contaminated with giardia as filter companies would have us think that there would be a lot more cases of illness.

HJ

Very good point. When I'm up at Amisk Lake in Sask we always drink right from the lake. The lodge gets their water there to with no filtration.

I agree, the waters here are very clean once you move away from civilization. There are very few cases of Giardia reported, however I still treat my water if I have any doubt as to it's source....especially in some low mountain areas where there are open range cattle grazing. That creek water may look and taste pristine where you are, however miles away and above you there could be herds of cows that have little disregard for sanitation practices...

There is a medical researcher here in California who is also a passionate backcountry enthusiast. He has access to a very high tech lab. He has, over a period of years, taken water samples from all over the Sierra Nevada. He's reached some interesting conclusions:
1. Water in the Sierra Nevada is generally safe to drink.
2. Water in the Sierra Nevada is generally cleaner than most municipal water supplies.
3. Giardia cannot survive the winter in the Sierra Nevada above 10,000' due to harsh freeze-thaw cycles.
4. Water near permanent human habitation is generally NOT safe to drink.
5. Water in areas where livestock grazing is permitted is generally NOT safe to drink.

I try to base my water treament decisions on the above. Close to trailheads or in heavily used areas, I treat my water. If there is livestock anywhere in the area, I treat the water.

On the other hand, in lesser used and remote areas, particularly above 10,000', I don't treat my water at all.

HJ

Interesting. I treat everything. (Or bring tap water from home for shorter hikes)

I wouldn't rely on them. They are only effective to 3.0 microns. That's only partially effective against the larger bugs: Crypto and Giardia, and completely ineffective against bacteria such as Salmonella and E.Coli (which have a much shorter incubation period). Sawyer makes a 0.1 micron in-line filter that can be bought separately or as part of their water filtering bottle. I use one of these filters with a Camelbak Bite-Flip cap on a Nalgene 1L water bottle as my standard day hike filter. It can also be hooked up in-line in the hose of a hydration bladder, and is easily field maintainable.

The First Need XL comes with a test dye. Add a few drops to your source water and pump through the filter. If the output water has any blue tint the filter needs to be replaced.