Both portable water filters and purifiers operate on the same mechanical principle. They suck up raw water from a contaminated water source and force it through a filtering medium to trap impurities - everything from sediment to invisible microorganisms. The clean water is then dispensed for use.
The difference between a water purifier and a water filter is that a purifier removes viruses(0.01 microns) as well as the bacteria(0.1 micron) and protozoa(1 micron) that filters can remove. Viruses are just too darn tiny to be removed with a filter so purifiers use either chemicals like iodine to kill viruses or an electro-static charge to capture them.
Lots of dudes will say that there is not much risk from viral infection in North America, but if you go abroad, then you have to be more careful. And, historically, to get rid of viral contamination in water, it was difficult, time-consuming, and expensive - but, hey, that's been changing! So, if you can get rid of everything and it doesn't cost much more and is not a real big hassle, then you might as well do it, right?
There are now quite a few water filters that add on a chemcial treatment to kill viruses - presto, a water purifier! And, the new breed of personal water purifiers that look just like soccer water bottles do a great job for individual use. But, they aren't too great for a backpacking crew.
So, you really have 3 options to purify your water while backpacking or hiking:
- Filter it, then boil it to kill everything. Boiling takes a long time and can give wate a bad taste.
- Filter first, then treat with an iodine or chlorine product. But, that can leave a bad chemical taste.
- Pre-treat with an iodine or chlorine product to kill everything, then filter to remove junk and the chemical taste.
Absolute Pore Size: A purifier will have a pore size rating in its advertising literature. A general rule of thumb is protozoa get removed above 1 micron, bacteria get removed above .1 micron, viruses get removed above .01 micron. The smaller the pore size, the more clean the water will be, but it may be more susceptible to clogging. Make sure you read the 'absolute' pore size rather then the 'nominal' pore size.
Filter medium: The material used to manufacture the filter cartridge greatly affects the quality and cost of a purifier. Materials are:
- Ceramic - an effective, high-quality earthen medium capable of repeated cleanings before requiring replacement. Just the very outer surface of a ceramic cartridge traps particles so a scrub brush is used to brush away clogged pores and expose new, clean ones. Ceramic lasts a long time but can be fragile and one crack ruins its ability to stop critters.
- Ceramic with carbon core - just like ceramic but the water passes over carbon after being filtered. This removes taste and odor from chlorine and iodine and some organic herbicides, pesticides, and chemicals.
- Glass fiber - very effective, less expensive than ceramic, but with a much shorter lifespan. These cartridges are usually pleated to increase surface area. Once they are clogged, they are replaced.
- Structured matrix - a dense, porous block of material that captures crud as the water is forced through the matrix and out the other side.
- Iodine resin - a layer of chemical integrated into the filtering medium to destroy viruses. It does not actually remove them, but kills them.
Pump Force: This gives an idea of how hard it is to push the handle in and out. A smaller number means easier pumping. 16 is pretty high.
Strokes per Liter: Tells how many times you need to pump to get a liter of water. A smaller number means more water per pump.
Instructions: Make sure you can read and understand the instructions. A unit should be simple to use, clean, and repair or it will be a waste of money. If the grammar of the instructions is too poor to understand, I would pass on that product.
Cost: You can get a cheap unit for $30 or something extravagant for $700. There are great ones available for around $100 that do an excellent job of producing safe, clean, virus free water. I wouldn't chance a cheaper product and I'm too stingy to throw away more money than I need to. Also, take into account the cost of any required chemicals.
Servicability: Some purifiers have cleanable filter elements, others you just replace the canister. Most all portable purifiers have moving parts that can wear out or break. Make sure you have replacement parts and know how to disassemble and re-assemble your gear. If service is a convoluted process, look for a different product. Products that include a service kit are a plus in my mind.
A unit should be servicable in the field, not requiring special tools or environment.
More to Consider
Here are a few more things to think about both when purchasing and using your portable water purifier.
- Make sure replacement cartridges are readily available and have an extra with you.
- Directly attaching to Nalgene bottle openings is a good feature.
- Cleanable ceramic filter elements is the best bet for gathering water for a group, especially for turbid water.
- Gathering water from a still, clear source is better than a turbulent stream that keeps particles particles and microorganisms suspended instead of letting them sink to the bottom.
- If you have free time and cloudy water, scoop water into a pot and let it sit for an hour before filtering. Then, only take the top 3/4s of water into your filter.
- If you notice human or animal activity, try to find a better place to gather your water.
- When you clean your filter, act as if you just used the bathroom. Thoroughly wash and disinfect your hands before doing anything else.
- Follow storage instructions for your purifier. Putting it away dry and sterilized is usually recommended.
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