Asked Question: "What is a water filter made for?"
This question could be asked in two (or more) ways: 1. Why do I need a water filter?
2. What does a water filter actually do?
In this post, we will examine these two questions.
1. Why do I need a water filter?
Simple answer - you want clean water.
Not-so-simple answer - the water in front of you may look purified, but it may not be. Residential water in the United States is mostly ok, with very rare exceptions. If you are looking at building your own house with a well, you would need to follow building code, and you would want to put in your own filtration/purification, but that is not the focus of this post.
In this post, we're talking more along the lines of: if you are out on a camping trip and wanted to drink water from a stream, lake, or *ahem* watering hole - or in emergencies such as if the city's water supply broke or was turned off, you ran out of your family water storage, and you needed to go find water from...a stream, lake, etc.
Wikipedia (the fountain of ALL wisdom, right?) has a good article about portable water purification that is really informative and actually has sources so you can double-check the information.
It says in this article, "large rivers may be polluted with sewage effluent, surface runoff, or industrial pollutants from sources far upstream. However, even small streams, springs and wells may be contaminated by animal waste and pathogens. The presence of dead animals upstream is not uncommon. In most parts of the world, water may be contaminated by bacteria, protozoa or parasitic worms from human and animal waste or pathogens which use other organisms as an intermediate host. Pathogenic strains of E coli bacteria survive briefly outside the body, to infect new hosts."
The article also mentions other pathogens and viruses that can be found in water that you would like to avoid. It's important to remove these pollutants, pathogens, and viruses from water that you want to drink. Otherwise, you can get sick very quickly - including diarrhea, vomiting, or even life-threatening cysts in the brain and liver.
Now that you want a filter...
2. What does a water filter actually do?
Again, in the article about portable water purification, it mentions several techniques for filtering/purifying water, and what these techniques actually do. Here is a list of the techniques, with a quick synopsis. For the full text, along with the proper procedures, please refer to the article.
Boiling
Boiling water will kill bacteria as well as other disease-causing microorganisms like Giardia lamblia and Cryptosporidium parvum which are commonly found in rivers and lakes.
Filtration
Portable pump filters are commercially available with ceramic filters that filter 5,000 to 50,000 litres per cartridge, removing pathogens down to the 0.2–0.3 micrometer (µm) range. Some also utilize activated charcoal filtering. Most filters of this kind remove most bacteria and protozoa, such as Cryptosporidium and Giardia lamblia, but not viruses except for the very largest of 0.3 micrometer and larger diameters, so disinfection by chemicals or ultraviolet light is still required after filtration.
Activated charcoal absorption
Charcoal is most commonly implemented for pre- or post-filtering, in a separate step than ceramic filtering, in either case being implemented prior to the addition of chemical disinfectants used to control bacteria or viruses that filters cannot remove. Activated charcoal can remove chlorine from treated water, removing any residual protection remaining in the water protecting against pathogens, and should not, in general, be used without careful thought after chemical disinfection treatments in portable water purification processing.
Chemical disinfection
Iodine used for water purification is commonly added to water as a solution, in crystallized form, or in tablets containing tetraglycine hydroperiodide that release 8 mg of iodine per tablet adaptation to chronic tetraglycine hydroperiodide. The iodine kills many, but not all, of the most common pathogens present in natural fresh water sources.
Ultraviolet purification
Ultraviolet (UV) light induces the formation of covalent linkages on DNA and thereby prevents microbes from reproducing. Without reproduction, the microbes become far less dangerous. A concern with UV portable water purification is that some pathogens are hundreds of times less sensitive to UV light than others.
Solar water disinfection
In solar water disinfection (SODIS), microbes are destroyed by temperature and UVA radiation provided by the sun. Water is placed in a transparent plastic PET bottle, which is first oxygenated by shaking partially filled capped bottles prior to filling the bottles all the way. The completely water-filled and capped bottles are exposed to sunlight, preferably on a corrugated metal roof, slanted slightly to maximize the exposure to solar radiation.
Solar distillation
Solar distillation may use a pre-manufactured and easily portable still, commonly referred to as a solar still, but it has its roots in a makeshift still that can be constructed simply from readily available components, typically being placed over a small pit that is dug into the ground. The solar still relies on sunlight to warm and evaporate the water to be purified. The water vapour condenses, usually on a plastic sheet suspended as an inverted cone, dripping into a collection cup placed beneath its center. For more continuous use, thin tubing or a hose is sometimes routed into the collection cup beneath the inverted cone, permitting repeated removal of water without disturbing the inverted cone upon which water condenses. In an extreme survival situation, a solar still can be used to prepare safe drinking water from usually unsuitable water sources, such as one's own urine, or even sea water.
Homemade water filters
Water filters can be made on-site using local materials such as grass, charcoal (e.g. from firewood burned in a special way). These filters are often used by soldiers and outdoor enthusiasts. Due to their low cost they can be made and used by anyone. The reliability of such systems is highly variable. Such filters can do little, if anything, to mitigate germs and other harmful constituents and can give a false sense of security that the water so produced is potable. Water processed through an improvised filters should be undergo secondary processing such as boiling to render it safe for consumption.
Summary
Now that you know why you would want a filter, and some ways to filter, make sure that you have a plan for filtering water if you run out of your water storage or get lost while camping, or any other emergency. Water is paramount to survival. You can only go for a few days before you will die from dehydration. Even just getting diarrhea will compound the problem because it dehydrates you even quicker, so it's important to have clean, filtered, purified water.
