You have the filter/purifier part right聴she聮ll need both in those areas. And that isn聮t a knock on Third World water standards. It聮s increasingly the case that a purifier is needed everywhere, the United States included.
Katadyn Pocket Filter
Pocket FilterI think the best way to approach this is through a two-stage approach. First, filter to remove grit, chemicals, and tiny creatures that can wreak havoc in your gut. Then, purify to kill viruses and other baddies the filter doesn聮t catch.
She聮ll be in these areas for at least a couple of years, correct? So I聮d get a really reliable filter. MSR聮s WaterWorks EX ($150; msrcorp.com) is sturdy, effective, easy to use, and easy to maintain. I聮d pack a spare cartridge ($40), membrane filter ($60), and maintenance kit ($20). Katadyn聮s Pocket Filter ($220; katadyn.com) is another excellent model. It聮s a little more rugged than the WaterWorks and equally effective at first-stage cleaning of water. Both units will remove chemical tastes, and catch nearly all measurable quantities of things such as giardia and cryptospiridia.
After the cleaning comes the purifying. The simplest way to achieve this is with MSR聮s SweetWater ($10 for a 2 oz. bottle, which is enough to treat 80 gallons). You add five drops of this stuff to a liter of water, mix it up, let it stand for five minutes, and drink. Potable Aqua ($8.50 for 50 tablets; potableaqua.com) works well also, but it can end up costing more than the SweetWater solution.
A good filter and water purifier is a combo that should keep your sister safe. And that聮s a wonderful thing she聮s doing.
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