I don't use a water filter so I can't comment, but if you do, you obviously should have a chemical back-up as well as a method to boil.
For chemical treatment, I really like the Micropur Tabs by Katadyn. See this website (
http://www.equipped.org/watrfood.htm) as it acknowledges the EPAs requirement of the labeling of 4 hours (which I have never done). 30 minutes and you are typcially good to go unless the water is particularly cold and/or bad. The tabs are really handy, I keep several duct taped to my water bottle as they are individually wrapped in foil.
While the tabs are relatively expensive, using 2% tincture of iodine is a low cost alternative. 5 drops per quart will take care of most pathogens except crypto (which is rare anyway).
Just to add to the discussion, adding these comments by RedWolfReturns at the Teaching Drum...
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So does this mean that we can train our bodies to resist giardia and other diseases?
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In my experience, yes. One of the main issues is to have enough non-harmful bacteria thriving in your gut so there's very little if any habitat for potentially dangerous bacteria. Antibiotics & overly sterile practices tend to wipe out the gut's whole ecosystem, thereby creating vast expanses for dangerous bacteria to populate once total sterility can no longer be maintained.
Awhile back they did a landmark study of Appalachian trail through hikers & found that the people who were hyper-sterile-obsessed about their water and the people who just drank water straight-up from sources all along the trail had about the same (very low) levels of stomach problems, while those who sterilized their water, but did so inconsistently had the most stomach upsets.
And when it comes to giardia, they've actually found that water transmission is rare. Most problems with giardia come from the oral-fecal route via poor sanitation & hygiene. Hygiene practices are very important in the wild.
Beyond that, a big issue is eating the right foods (lots of fat, protein & fiber, not much sugar & simple carbs) in the right quantities (stuffing your gut is a bad habit, while eating frequently in small amounts is a better habit) so the bacteria levels in your gut stay in balance. Bacteria (and yeasts) can eat sugar straight-up, thus they feed on your food at the same time you do. Stuff yourself with sugar (or eat sugar after stuffing yourself with other foods) and you've just diluted your own stomach acids and created a feast for the little guys in your gut.
Also, it is important to understand how bacteria populates water...water close to shore is likely to have higher bacteria content than water farther out, and colder water (esp in winter) has less bacteria than warm water. Tannic water has less bacteria than non-tannic water. Moving water less than stagnant water. Also, springs are natural filters.
Put all this information together in a synergistic way, and you've got a recipe for drinking wild water safely.
Here at the Teaching Drum we take about a month to slowly wean our students onto wild water (slowly building up their tolerance to the new bacteria), and from then on they drink it the rest of the year with no problems (unless they violate our camp hygiene guidelines or sneak into town and stuff themselves on sugar, bread & beer... ).
