Well, heck, Dale, if you're considering gravity filters I have to say something that I've said many times before:
I don't understand why more people aren't using Sawyer filters.
Once I tried them I knew I was never going back. They use a microtubule technology similar to dialysis kidneys (and, IIRC, the MSR Hyperflow.) You can buy or rig a gravity filter setup, or a sip-from-the-filter-in-a-bottle setup, etc. The newer models have quick-detach adapters so it is easy to switch the filter between setups. They provide excellent reductions on protozoans, bacteria, and viruses. In fact there are two versions, and the more fine filter qualifies as a water purifier (rather than a mere water filter) by federal standards. They have a million-gallon guarantee (it used to be a lifetime guarantee, but they figured they needed to just pick a number), so the filters don't really go bad unless damaged or frozen. It certainly could last a lifetime. They are brutally simple, and thus durable.
I have no affiliation whatsoever with Sawyer. Just sayin'.
As I mentioned the HyperFlow uses the same basic technology, I think. But when I was shopping around a couple of years ago it was getting really bad reviews. They may have fixed the problems by now, but it had durability issues.
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I agree, the MIOX has none of the advantages of other chemical water treatments, all of the disadvantages of other chemical water treatments, invents at least one disadvantage of its own (primarily the need for batteries and for salt refills), and weighs as much as some filters. I've never been a fan. The one situation where it probably excels is in treating very large volumes of water when used as the sole purification device for a large group.
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What was spam? I hope not Katie. After all her very first sentence gives the disclaimer that she is a MIOX employee. I don't think that her post was out of line, per se.
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I was getting ready to jump all over the filters-vs-chemical comments, but then saw that Paul covered it in detail.
Heck, if anything viruses are the WEAK point of filters- many don't do a good job against particles that small. Viruses are where chemical treatments EXCEL.