Filtering and Purifying an Unknown Water Source

The point of this article is to outline the process of filtering and purifying a water source. In an emergency situation, you may need to rely on water from an unknown source- a stream, a lake, a well, etc- for survival. You’ll want to clean this water of contaminants before drinking it to avoid unwanted illness.

As a side note, the best water source in an emergency is the one you prepared BEFORE the emergency. While filtering and purification will greatly reduce contamination, it’s rarely 100% and there’s always a chance you can get sick. You can avoid this all together by preparing a water source ahead of time. Considering how cheap (essentially free) water is, there is no reason every household should not have at least 3 days worth of water stored for every person. For more information on how to do this, check out this article on emergency water supply and storage.

Choosing the correct type of unknown water source is important

But suppose your water supply has run out, or you find yourself in the wilderness, and you must rely on an unknown water source. When selecting one, go with the cleanest, salt-free water source first. Cold water is better than warm, and running water is better than stagnant.

Let’s take a look at some of the water contaminants we need to be concerned about, and then how to get rid of them.

Possible Contaminants

There are two kinds of contaminants we need to look out for: pathogens and pollutants.

Pathogens are tiny living organisms that live in the water. Most are harmless, but a few of them can wreak havoc on the human body. The largest form of pathogen is protozoa, the group parasites belong to. Some of these we need to worry about are Giaridia Lamblia and cryptosporidium. Bacteria are the next smallest pathogen. Some of these we need to worry about are E coli, cholera, and salmonella. Viruses are the tiniest of pathogens. Some of these we need to worry about are Hepatitis A, Norwalk, and Polio.

Pollutants are any man-made substance that is harmful to the human body. Various forms of chemicals, fuels and sewage fall into this category.

Coming into contact with any of these contaminants can result in various symptoms, including fever, nausea, dehydration, fatigue, cramps, diarrhea, and even death. So it’s important that, if we’re going to drink this water, we find a way to filter and purify it.

Filtering Water

The filtering process is meant to remove larger particles and pathogens from the water.

For larger visible particles, straining with a paper towel of coffee filter should be enough.

For smaller contaminants, we want to use a filter with smaller pores. Some of the options available are these:
(Note: a micron is 1/1000 millimeters)

Ceramic: The best option, but the most expensive. It has pores in the 0.1-0.5 micron range.

Glass fiber: The next best option, and much cheaper. Its pores are in the .2-1.0 micron range.

Compressed Surgical Paper: Similar is price and pore size to glass fiber.

Hard-block carbon: Has larger pores, so less effective at filtering particles and pathogens. It is effective, though, at absorbing some chemicals and pollutants. As such it makes a great step in the filtering process, but shouldn’t be the whole process itself.

Purifying Water

The purifying process is meant to remove the smaller particles and pathogens that were missed during the filtering process.

Boiling: Boiling for an extended period (some recommend 3+ minutes, some say up to 10+ minutes) will kill all pathogens, and it’s cheap and easy. There are a few downsides, however. The fuel or electricity needed to boil water may not be available during an emergency situation. Also, it’s impractical to boil anything more than small amounts of water. Lots of the water is lost through steam (which will be a problem if your water supply is limited), and it takes a long time to cool down.

If boiling water isn’t an option for you, some alternatives are:
2% iodine solution: is pretty cheap and will kill most pathogens. Use 3 drops/quart of clear water, 6 drops/quart of cloudy water. Stir and let sit for 30 minutes before using. Water purified with iodine should not be used by pregnant women, and iodine should not be a long term solution as it can be toxic in large doses.

Chlorine (use unscented household bleach with 5.25% sodium hypochlorite): another disinfectant solution. It’s very poisonous, so make sure you get your doses right. Add 2 drops for every quart and stir and let sit for 30 minutes before using again. The water will have a light bleach odor.

UV lamps: Ultraviolet radiation can destroy pathogens ability to reproduce, and it’s effective across the board, from the largest to the smallest pathogens. UV purification is great to have as a stage in the cleaning process. Requires electricity, though, which may not be available in a lot of emergency situations that require water purification.

After filtering and purifying your water source, that water should be good to drink.

Good luck and stay prepared!

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