First letís go over the difference in what a filter and a purifier are. A filter will take out microscopic organisms by pushing the water through some sort of screen or filter. Now donít worry; these filters are extremely small. You will often here a filter rated as .2 microns. What this means is that the holes in the screen are 2 x 10^-6 meters, or for non-technical people, the holes are pretty darn small. A purifier does the same as a filter by pushing the water through some sort of screen, but then it also adds a hint of iodine to kill any living organisms.
So by now you are asking yourself, "Should I get a filter or a purifier?" And the answer is really, it doesnít matter too much. Each will provide you with plenty of protection. If you are going to go on a long trip of over a week or you will be near known contaminated water, you might want to choose a purifier. This just adds a little safety factor because you donít want to get intestinal problems that can spoil a trip. But if you are going out just for day hikes and short trips, then a filter should be more than adequate.
A few other things to look at when buying a filter is the pump rate, or how fast it pushes the water through the filter. See if you can replace the cartridge in your filter. On average for a Pur Hiker or a Sweetwater Guardian (the two leaders in the market) the cartridge generally can pump 100 gallons. During the life of the cartridge be sure to clean it just to extend its life.
Now if you are still a little wary about filters, you can always go back to the good ole iodine tablets. One quick iodine tip, if you are using the iodine tablets or a purifier that adds iodine and have thyroid problems, then consult your doctor. Sometimes iodine can adversely affect it.
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