I should emphasize that I don't own all of these treatment types, haven't used all of them, and I don't have access to a lab capable of testing all of the claims made by the makers. These are my opinions of the filters as well as my opinions of their claims. Think of it as your free helping of ice cream for the day.
Pasteurizing or boiling water requires nothing more than a container and a source of heat (usually a fire), two things that you're likely to have readily available. Boiling your water will take care of the biological contaminants, but will have little effect on the chemicals present. I consider this the bare minimum level of treating water that I don't know to be potable.
Good for disinfecting water (killing anything in it), chemical treatment takes up very little room in a bag but generally has little to no effect on chemical contamination. Most chemical treatment types take 10 to 30 minutes to work, so they are not the best for quick treatment. They also tend to leave an “off” taste in the water (if used properly) which may be a disadvantage for some people. I consider the various tablets a good system for disinfecting clear running water I might find in a stream, small river, or some source that I'm just not sure about.
- Potable Aqua: Iodine-based tablets, cheap and compact. Coleman markets a two-step system that uses Potable Aqua tablets and a second tablet that removes the Iodine taste, if that's a serious problem for you.
- Taharmayin: Non-iodine based tablets for people allergic to Iodine, they still take 30 minutes to work. Can also be used to disinfect food and wounds in a pinch.
- Katadyn Micropur: Chlorine dioxide-based tablets. Less of an aftertaste than Iodine, but just as effective. Costs about twice what you'd pay for Iodine tablets.
- Bleach: Double-acting with both chlorine and oxidizing components, very easy to find but with a limited shelf life. Make sure you only use unscented bleach for your water treatment.
- Potassium Permangenate: More stable than bleach, has multiple uses, and is cheap but not as easy to find. Permanganates are also strong oxidizers and must be stored with care to avoid unintentional fires and corrosion.
Easy to stick in a pocket and light enough to be barely noticeable in a pack, filter straws are generally cheap ($20.00) and come with a range of quality that bears paying attention to. Spend a few extra dollars if you plan on using a straw filter for more than taking bad tastes or odors out of tap water! Pros: No pumping to get clean water and most use no chemicals. Cons: Very limited life but convenient to have in time of need.
- LifeStraw: 250 gallon life, weighs 2 ounces, log 6 (99.9999%) removal of bacteria, 99.9% removal of protozoa and 0.2 micron filtration. Not rated for virus removal, therefore not recommended for water that may be polluted with human sewage.
- Aquamira Frontier: 50 gallons life, weighs about an ounce, 99.9% Giardia removal. ALso not rated for virus removal.
- Banyan Emergency Filter: 200 gallon life, weighs less than 2 ounces, claims 15 micron filtration but also claim log 7 (99.99999%) removal of protozoa which doesn't add up. 15 micron filtration is pathetic, so I'm not sure if it was a typographical error or if they're just trying to make it sound better by using scientific jargon.
Larger than the straws, providing longer life and often using more than one type of treatment for better removal, pocket filters generally cost more than the straws or tablets. A better choice for when you expect to need to treat you drinking water for more than a few days, this type is a good example of the middle ground available. Pocket filters come in two general types, Reverse Osmosis (RO) and micro-filtration (standard).
Standard type: uses micro- or ultra-filtration media to separate the water from the contaminants. Efficiency of the filter media will vary widely according to the manufacturer, and should be compared closely to similar units before purchase. Avoid systems made in areas with a history of little to no regard for quality control, since it is your life on the line.
- The Sawyer Mini is what I currently have in my bags. Small, light (2 ounces), cheap (<$20), and performance good enough for the water I will find in my area. The 0.1 micron filter is among the best on the market right now, but I'm doubtful of their claim of 100,000 gallon filter life.
- Katadyn makes a selection of pocket filters for the backpacking market. They are generally well-built and moderately expensive ($75-300) depending on which model you're looking at. Filter efficiency varies by model, with 0.2-0.3 micron being normal. Some models come with carbon stages, silver impregnated ceramic, or built in pre-filters depending on what you're looking for and are willing to pay.
- MSR Miniworks is a good example of a multi-stage filter. Using ceramic and carbon filter media, it is capable of removing anything larger than 0.2 microns as well as chemical contaminants. Less than $100, it's a good choice for rugged camping and backpacking.
RO systems: generally sold as desalination filters for sea water, these take a lot of energy to operate and produce less (but cleaner) water than a standard filter. If it has a long pump handle on it, it is usually some sort of RO system. There aren't many potable options that I can find, but you may have better luck if you live nearer an ocean (I'm about 1000 miles from the nearest).
- Katadyn Survivor series: Internationally-known and -used manual desalination kits that are Coast Guard issue, not just CG-approved. Expensive units, with the larger (multi-person) running $2000 or more. The smaller one is $300 and will produce about a liter of water per hour of pumping.
There are a lot of “sport” bottles with integral filters in them on the market. Most are made in China, with very little to no actual data available on their efficiency or method of filtration. From what I have seen, most are designed to remove bad tastes from tap water, so they likely use a resin or carbon filter to remove the residual chlorine from tap water and maybe some of the metals. I have to place them in the same category as the pitcher-type filters, and can not recommend their use for cleaning up untreated water with the exception of the LifeStraw version. If you see words like “fresh tasting”, “fresh and tastes great”, and no mention of removing bacteria or protozoa it is time to keep looking.
When you have to treat water for a large group, for a long time or in a stable location, the options get larger, and usually more expensive.
- First Need: My first water filter. I bought one of these over 20 years ago to use on camping trips and it is still being made and I can still get parts for it. 0.3 micron filter with a pre-filter on the hose and threaded to fit common Nalgene bottles, it is a hiker's filter. Too large to drop in a pocket and weighs more than a pound, but it puts out water twice as fast as comparable filters. Rated for 200 gallons of use, but can be back-flushed to extend the life. I know this filter can take the color out of fruit juice, but not the sugars; that's an example of 0.3 micron efficiency.
- Berkey: If you want a good quality, well-known and respected name, and a filter that is designed for use in a static location, look at the Berkey line. They do make smaller, more portable filters, but they got their reputation making base-camp equipment. Large, heavy, and make of metal, the body of their filters are sturdy. They use a ceramic filter media that is easy to clean and are rated for 500+ gallons of use. They are also expensive, but many find them worth the money.
- Just Water is a resin and ceramic filter block that is designed to be installed in a gravity (drip) filter made of two plastic five-gallon buckets. Not expensive, they were originally designed for use in third-world countries and have had mixed reviews here in the US. Being ceramic, the filter media can break if not handled with at least a bit of care.
- Katadyn makes a “base camp” level system, if you like the brand. 200 gallon filter life, up to 10 gallons per hour.
- Platypus GravityWorks is another brand of gravity fed filter. Rated at about 20 gallons per hour, and using a replaceable in-line filter, it would be a good choice for a large group setting.
If you can set up a still, you'll be able to clean up your water. Be aware that a still won't take out all of the chemicals that may be present, but will definitely take out all of the biological contaminants. The main use I can foresee for distilled water would be for medical uses, where you want water to be sterile. Boiling might work, but distilled would be better.
- Aquamate solar still, which is an example of the type of desalination still available, costs about as much as a Katadyn RO system. Produces 0.5 to 2.0 liters of water a day depending on the sunshine, which is barely enough for one person. Yes, they're easier to use (no pumping), but they don't have the output needed for multiple people.
- Non-electric stills like the Survival Still work over a camp fire or stove and put out about a half gallon of clean water per hour.. They are useful, but consume fuel that may be better used elsewhere, depending on your circumstances.
- Electric stills like those made by GOWE are more suited to a laboratory than a survival situation. Requiring 220V AC power, they will put out very clean water, but if the power goes out you're stuck with a very expensive (>$500) door stop.
I hope someone out there finds this information useful, or at least learns enough to be able to ask the right questions when shopping for water treatment options. Always remember that it's your life on the line, not the salesman's, and shop accordingly. Water is second only to air for your survival and needs to be taken seriously. Don't let anyone convince you to settle for less than the very best that you can afford! Read, research, and ask questions now while you have the opportunity.