Waterfilter: Help me understand water purification

November 24, 2005 8:44 PM

WaterFilter: I'm looking into water purification devices. I'm mostly trying to understand what might help with various kinds of contamination threats: What would I buy to safely drink from a mountain stream? Is there anything that can help with chemically poisoned waters if one were, say, trapped in New Orleans by Katrina? Radioactive fallout contamination?

I am thinking of buying such contraptions soon, but've never had anything beyond a Brita pitcher for the fridge to take the edge off of dubious LA urban tapwater. I'm looking with an eye to both recreation purposes and survival. I'd like to understand principles involved, but I wouldn't mind pointers to specific products.

posted by namespan to science & nature (11 comments total)

The Lifestraw would be a good start, if it was being sold.
posted by bh at 10:15 PM on November 24, 2005

What, you're putting together a go bag? Those are each vastly different types of threats.

There are chemical sanitizers you can buy for mountain water, and you can boil with the right equipment, and you can boil and filter. These are routine for any backcountry enthusiast.

For radioactivity, the best solution is to avoid contaminated water as much as possible. Don't drink reservoir water near an airburst, and wait until after rain has cleansed the air of dust before turning to rainwater. For the immediate future well water and any kind of tanked water will be safe. Failing that, iodide pills are essential for children or young adults to prevent thyroid cancer.

Water such as New Orleans in the "bowl" is probably not safe in any way, and the contaminants could vary widely from one area to another. Everything from antifreeze to industrial cleaners to oils and God knows what else, and we haven't even touched on biological contamination. Even so, modern medical treatment can do wonders for ailments such as dysentery and cholera, as long as they're not so widespread as to be a public health emergency by themselves. In the 19th century, outbreaks were common and frequently fatal, leading to massive engineering projects such as reversing the Chicago River.

In Harbin this week, they're shutting off the city's water -- for millions of people -- because of a massive spill of benzene upriver. (I wonder whether it would be at all possible to reduce the spill's effects by containing it -- it should float -- and trying to burn it, like the Cuyahoga River used to ...) That's just stay-the-hell-away stuff.
posted by dhartung at 10:47 PM on November 24, 2005

There are various types of filters. Popular brands include Katadyn, Pur, MSR etc. and you can check them out at REI, EMS or similar places. They have various levels of complexity, field repair-ableness, capacity (gallons per hour), weight and cost of replacement filters. Most people are passionately attached to their brand so ask around and don't just take the salesman word for which is the best. The most common is the handheld pump which is ideal for back country travel. By "ideal" I mean fiddly, prone to breakdown and generally designed to be operated by a three-armed person. If you take a filter into the back country always take a back up supply of iodine tablets or bleach. You want one that has an attachment to allow you to pump directly into a Nalgene or other bottle, otherwise you will actually need more than three arms to operate it.

You can also get filters that are built into water bottles like this one. These are useless for sole use as you can't make enough water to cook or even drink easily. They are really for dayhikes, back country running etc. Finally there are much larger gravity fed filters- useful for base camps and probably the most suitable for natural disasters.

Most filters remove bacteria and amoeba type things (giardia etc.) and are fine for back country or general use. You can also get "purifiers" that remove or kill viruses: these are more expensive and harder to pump water through. The cost of back up and replacement inserts is a consideration as they rarely last as long as claimed and it's easy to totally clog one by filtering muddy or silty water through it at which point it is useless. The recleanable ones are nice, except they tend to be ceramic so if you drop 'em they break.

I have an older Pur and I like it but it is totally clogged at the moment. I just hope I can still get filters for it- that's anothr thing to think about, if you're going to be traveling abroad can you easily get the replacement parts there?
posted by fshgrl at 11:04 PM on November 24, 2005

The majority of water purifiers on the market will fall into two basic groups: chemical treatment or filtration (or a combination of both).
Chemical systems are avoided by many because of, well, the chemicals. Filtration devices will use a variety of materials in the filter from plain ceramic to carbon and combinations. Especially important when purchasing a filtration system is the micron size which it will filter out.
Your best bet, in most cases is to use a combination of both as long as you don't mind a little chemical taste (try putting a slice of lemon or lime into the water to counter it a bit).
A good guide to how different purification methods work can be found at the OA Guide to Water Purification.
When it comes to unnatural contaminants, there is no fullproof method. Your best bet (and most expensive probably) is the MIOX Purifier from Mountain Safety Research (MSR). They developed this device with the U.S. Military as a portable method of oxidizing water. Oxidizers have been around for a while, but are usually found in municipal water treatment facilities and wouldn't fit into your backpack, or even your Hummer. It basically is a battery powered cell that oxidizes a small cap full of water using a salt tablet. When this sample is added to your water (ideally filtered through another device first) it starts a chain reaction of the oxygen in the water and starves off viruses, bacteria, Giardia, and Cryptosporidium.
It has been used by troops in areas with chemical warfare threats, so it can probably be trusted for just about anything you might come across. (Not sure I would dip my Nalgene into a radioactive stream in any case, however.)
The best purifications systems are probably either something from MSR or, for a bit more cost, Katadyn, who make systems for larger volume applications.
posted by medium format at 11:07 PM on November 24, 2005

I have a Pur hiking filter. It is a combination of filtration (like a strainer), and chemical (iodine). It has a charcoal filter as the last stage to mostly eliminate the iodine taste. It is good against most bacteria and viruses, and some chemicals and metals and what not (if I remember correctly).

It ceases to function when the filter is worn out -- the filtration unit is replacable.

As fishgrl mentions, it's a bit of a pain to use. It is recommended for everything but raw sewage by Pur. For a situation like Katrina, though, it'd be a gamble, but certainly better than nothing. It'd get the living stuff, but who knows about other pollutants of the non-organic variety.
posted by teece at 12:02 AM on November 25, 2005

fshgrl, Pur was bought by Katadyn a couple of years ago. They have changed the filters on the newer models of the Hiker, but I believe you can still get replacements for the older models.
posted by medium format at 1:08 AM on November 25, 2005

Previously.
posted by jjg at 8:16 AM on November 25, 2005

You might consider a disteller rather than a filter. I'm not 100% sure that it would get rid of all the chemicals in polluted water, but it'd do a lot better than most filters on the market. Also there's no replacement parts. The downside is that it's not very portable.
posted by electroboy at 10:18 AM on November 25, 2005

When I was backpacking, we used Pristine. We never got ill from bad lifeforms. On the other hand, there's also no guarantee that the water we were drinking was unhealthy to begin with.

Not very useful with murky water and useless if the water is chemically contanimated.
posted by five fresh fish at 10:55 AM on November 25, 2005

Radioactive fallout contamination?

Potassium Iodide stems the body's natural absorption of radiation, and might buy you a few extra days in a not-too-terribly contaminated area.
posted by Civil_Disobedient at 3:39 PM on November 25, 2005

Both distillation and reverse osmosis should be able to cut/eliminate radioactive contamination of water.
posted by Good Brain at 4:51 PM on November 25, 2005