Water filter
From Trail-Finder -- Dedicated to getting you outside
Contents |
Overview
Water filters are one of the easiest ways to purify surface water you find in backcountry to make it safe for drinking. There are many water filters which are suitable for backcountry use. These filters are not the same water filters which are suitable for household use, however, as household water filters are assumed to start with drinkable water while backcountry water filters are assumed to be used with water which is not safe to drink.
For purposes of backcountry use, water filter and water purifier are generally used interchangeably, however only water purifiers should be used in backcountry, as all surface water should be assumed to be contaminated.
Water filters work only with fresh, not salt, water. To make salt water drinkable, you must first use some form of distillation, such as a solar still.
Components
- Filter Matrix: All water filters must contain a filter matrix. This material is generally made of a dense ceramic or carbon matrix, and is the heart of the water filter. Everything else is just used to move the water through the matrix. The best filters have a field-serviceable and/or back-flushable filter matrix.
- Casing: The filter matrix is fragile, so must be enclosed in a durable, rugged housing. These are normally high-impact plastic.
- Pump: Water filters must be fed either by pumps or gravity feed. Pumps are the most common. The pump should be easy to use with one hand, since you will often be crouching on the side of a stream, holding the pump, filter, and your water bottle, all while trying to not fall into the water. The pump is often solidly attached to the filter casing, and may be field serviceable.
- Pre-filter: Pre-filters are large-pore filters useful for filtering out mud, dead leaves, etc. They prevent that stuff from getting into your pump or filter, where they will quickly make them unusable. Some water filters come with pre-filters. If your filter doesn't come with a pre-filter, you should consider adding one. They are quite inexpensive, and far cheaper than replacing your filter inadvertently sucking up some debris in your pump.
- Bottle filler: Basic water filters just dump the filtered water out the bottom or through a piece of plastic tubing. Some, however, have screw attachments for attaching different types of water bottles.
- Plastic tubing: Except for small, one-piece water filters, plastic tubing is used to move the water from the pre-filter, through the pump, into filter matrix, then out to your water bottle. This tubing is fairly destructible, but fortunately, it's also easily replaceable. Replacement tubing can be found in the plumbing section of any good building materials store for only a few cents.
Effectiveness
Water filters all include two, critical numbers. If you don't see both, you probably shouldn't buy the filter. These measurements are given in microns, or 0.000,001 meter.
- Absolute microns: This is the absolute largest particle which can find its way through a pore in the filter matrix. 0.4 microns or smaller is good.
- Nominal microns: Since the filter matrix is like a tight, twisted maze of holes and passages, so even though the absolute largest particle which can fit through may be 0.4 microns, the effective size of any particle which is likely to make it is likely much smaller. This is referred to as the nominal size. 0.1 microns is good.
Other water filters use a combination of mechanical and chemical filtration. This allows for a slightly larger pore size in the filter, with a chemical substance killing off the remaining virus and bacteria. These filters are often less expensive, but may give water with a chemical aftertaste. Also, once you run out of the chemical additive, your filter may no longer provide safe drinking water.
The final option is newer on the market, and not as commonly used. Using UV radiation, it is capable of killing virus, bacteria, and other microbes, like giardia and cryptosporidium. It does not, however, have any effect on chemical or radioactive contaminants.
Lifespan
Water filters are generally sold with a stated lifespan, be it 50 gallons or 200. To extend the lifespan, filter only clear, sediment-free water whenever possible. Also, if your filter is dropped hard, or if you ever hear a rattle from it, unless you can visually verify that the filter matrix is undamaged, assume the filter is no longer going to provide safe drinking water.
Alternatives
Water filters are among the best options for a nearly unlimited supply of fresh, clean, safe drinking water in backcountry. Other options include:
- Chemical water treatment: Adding purification liquid or tablets to a fixed amount of water, then waiting a minimum time, kills biological contaminants in the water. They also generally leave an unpleasant taste. Good for emergency kits, since they take very little room and weigh practically nothing, but they aren't used much anymore.
- Boiling: Bringing water to a rapid boil for at least five minutes, longer at high altitude, will kill off biological contaminants.
Categories: Gear | Water
