Whether it’s a pristine alpine stream or the Hudson River, the water you find from natural sources really should be treated as if it’s not potable. There are definitely natural spring water sources or glacial runoff that are potable, but without a microbiological assay you can never know for sure. It’s very unlikely that you’ll be the first living being to come across these water sources, and the thing about squirrels, beavers, chipmunks, wombats, lemurs, or what have you, is that they poo. And pee. And sometimes they do it right upstream. So what exactly are we treating our water sources for? Water contaminants may be microbiological in nature, including protozoa, bacteria, viruses, and parasite eggs. They may be aesthetic, either from sand, silt, or mud. They may be chemical in nature, ranging from harmless but disgusting sulphur compounds all the way to organic pesticides, fertilizers, or halides like chlorine. Not every filter or treatment is designed to remove all of these compounds, and many focus purely on the microbiological contaminants, as most remote water sources are fairly clear, tasty, and free from farm runoff or other chemicals. So, what are the options available to us?
Heat treatment: Boiling water is a sure-fire method to kill any microbiological contaminants, but it does require fuel and a pot to boil your water in. The old adage was to boil water for 5 minutes, but just bringing the water to a boil will kill most harmful microorganisms. Boiling doesn’t remove anything from the water, however, so if your water is silty, turbid, or stinky, you may want to filter the water through something like a bandana beforehand, and deal with the smell. It builds character.
UV treatment: There are a couple of different options on the market that utilize UV light to sanitize water, including the Steri-Pen and the Camelbak All Clear. These work by ruining the DNA of any microorganisms in the water and preventing them from replicating. For you science dorks out there, it works by turning adjacent thymine molecules into dimers, which show up as broken parts of the DNA code–this is the same process that causes skin cancer from excessive UV exposure. These treatments require batteries, and like boiling water they do nothing to improve aesthetics, but they do so at any temperature and work in only a couple minutes of stirring or shaking.
Chemical treatments: Most chemical treatments will be from the halide group of chemicals, and will include either iodine or chlorine based solutions. While these are effective against most microorganisms within 15-20 minutes, cryptosporidium may require prolonged contact of as much as 4 hours to work. Iodine treatments like Polar Pure leave a small iodine taste in the water, which can be easily masked with flavorings like Gatorade or other drink mixes. Chlorine, especially chlorine dioxide treatments like Aquamira, leave no scent or smell in the water, and may be safer for long-term use (say, hiking the PCT).
Mechanical Filters: Mechanical filters fall basically into three categories, glassfiber or paper-pulp filters like the Katadyn Hiker Pro or the First Need XLE, ceramic filters like the MSR Miniworks EX, or hollow fiber filters like the MSR Hyperflow and Platypus GravityWorks. Some fiber filters like the Hiker Pro are inexpensive and fairly fast, but can’t be cleaned, and will slow over time until the filter needs replacement. The First Need can be backflushed, and is the only mechanical filter certified to remove viruses, making it an excellent choice for people traveling to third-world countries where waterborne viruses are more common (it’s unnecessary in the continental US). Both of these filters utilize activated charcoal and will remove organic chemicals and make the water taste better. Ceramic filters are slow, but very durable, and can last for thousands of gallons. They must be cleaned frequently, but they offer the same performance across the lifespan of their filter. They also include activated charcoal.
The newest technology on the block, hollow fiber filters, are the fastest the market, offering flow rates of several liters per minute. They can be cleaned by backflushing the filter, and are very light and compact. They’re so fast that they can easily be used without pressure from a traditional pump, allowing the Gravityworks to be the fastest hands-free filter on the market. With a pump, the Hyperflow can produce as powerful of a stream as a home faucet. Neither of these filters utilize activated charcoal, and therefore will not remove any chemicals or odors from the water.