Water Purification: 4 Things You Must Know...

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Water: the source of life. One can live weeks without food, but only days without water. Water makes up approximately 60–70% of a human’s body weight. It is, and should be, one of the most important considerations in planning for a long-term disaster scenario. Given that the average human will need one gallon per person per day minimum, storage of large quantities of water quickly becomes impractical and therefore won’t be discussed in this post. This article also assumes that you don’t have a private well that is completely off the grid. If you have the land, if the city or county allows it, and if you can afford it, then by all means, make getting a private well your first order of business!

So how can one find safe water after a major disaster? If you don’t have a well with a solar or hand pump, you’ll most likely have to rely on natural sources of water such as streams, ponds, lakes, or rivers. It would still be quite dangerous to drink directly from stream or river, even if it appears completely clean and clear. There is always the risk from Giardia and Cryptosporidium, not to mention the chance of a dead animal just upstream unbeknownst to you. Even a bit of animal or human excrement upstream can make a person seriously or deathly ill. If you use natural sources of water, then some form of filtration or purification will be necessary.

So, what to do? Well, you have a few options:

1. Filters

First, you could invest in a ceramic filter, like the British Berkefeld Ceramic Water Filter. While a bit pricey, they’re both highly recommended and receive terrific reviews. I’ve used this particular brand in West Africa for many years, and I admit they are convenient, safe, effective, easy to maintain, and long-lasting. The ceramic filters only need an occasional cleaning and can withstand cleaning many times before needing to be replaced.

Big Berkey BK4X2-CF Wi... Check Amazon for Pricing.

They are definitely worth the money, but you should note that they only filter out organic contaminants and sediment from water. Since they don’t have anything like activated charcoal, they don’t filter out chemical contaminants. I don’t imagine most sources of water would contain dangerous levels of chemicals, but if you take water from a river or stream that is next to a typical commercial farm, there is the risk of ingesting pesticides and herbicides from the farm runoff. It’s the same for water that near an industrial plant. This should not be a problem for most people, but it is good to be aware of the possibilities. Know what is upstream!

For a good portable filter, you could go with the Swiss-made Katadyn Hiker or the Hiker Pro. A wonderful benefit to these filters is that they are extremely portable, which makes them vital components of bug-out bags. Another benefit is that they remove virtually all organic and chemical contaminants.

The down side is that you only get about 200 gallons out of each filter, and the replacements add up very quickly. However, if you want more filtration for your money, like say 13,000 gallons worth, you can go with the Katadyn Pocket Water Microfilter. While remaining very portable, it uses a simple ceramic candle similar to the British Berkefeld. Just note that as with all ceramic candles, it won’t filter out chemical contaminants.

An interesting, albeit more primitive option, is to build a BioSand Filter. They’re not perfect, but they are so rugged and easy to build and maintain that they are worth some consideration. They remove around 95% – 99% of all organic contaminants by way of an active “biological layer” and simple sand filtration.

Katadyn Pocket Water F... Check Amazon for Pricing.

These filters have largely been implemented in the humanitarian realm by organizations such as Samaritan’s Purse and Convoy of Hope. You can build them out of plastic or concrete, and they’re very low maintenance. Again, they don’t remove 100% of organic contaminates, so there’s still a very small chance of getting a water-borne bug of some kind, but it’s a good semi-permanent solution when your other options run out.

Katadyn Hiker PRO Wate... Check Amazon for Pricing.

Since the biological layer takes some time to develop, you could use other short-term methods listed here to carry you over until this filter is fully functioning. They really do save lives in the third-world, so it’s worth some investigation, at least for a backup option. You can find plans online for building them.

2. Boiling

There’s always the idea of boiling your water, but for that you would need a large source of energy, perhaps something like wood or propane, not to mention a large amount of time as well as storage. Boiling water may work in a pinch, but it would be extremely cost and resource prohibitive in the long run, especially in a long-term grid down scenario.

On a personal note, many years ago, I went on a weekend camping trip and severely underestimated my water demands, all while carrying foods high in sodium. Needless to say, I became very dehydrated and had to stay up all night boiling, cooling, and drinking river-water. It worked great, but due to the time and the energy necessary to boil water, I quickly realized that relying on this method of water purification in the long-term is not a good idea.

3. Chemical Disinfection (i.e. Chlorination)

In a common local disaster scenario (hurricane, ice storm, tornado, etc), organizations such as FEMA and the Red Cross suggest using unscented household bleach (5.25 to 6.0 percent sodium hypochlorite) to treat water. FEMAs instructions are as follows:

“Add 16 drops (1/8 teaspoon) of bleach per gallon of water, stir, and let stand for 30 minutes. The water should have a slight bleach odor. If it doesn’t, then repeat the dosage and let stand another 15 minutes. If it still does not smell of chlorine, discard it and find another source of water.”

This method is not really generally recommended for long-term use. Plus, bleach has a limited shelf-life (around 6 to 9 months), so you’d have to rotate your supply often in a long-term disaster. To get around this limit, some people instead buy calcium hypochlorite (rather than the sodium hypochlorite in bleach) in the form of “pool shock.” It comes in granular form, is relatively stable, and has a surprisingly long shelf-life.

I’d be careful with this stuff however, as storage can be dicey (I’ve heard stories of it corroding surrounding items when not stored properly), and one needs to be aware of proper measurements and mixing amounts. I’m sure with enough research and preparation, the granular calcium hypochlorite could be a fairly good backup method of water purification.

4. Solar Disinfection: SODIS

SODIS, or SOlar DISinfection, is the cheapest and easiest of the methods listed here. Solar disinfection only requires two things: clear plastic (PET) bottles and sunlight. Find soda or water bottles with the PET recycling mark that are clear and colorless, 2 liters or less in volume, and preferably no more than 4 inches in diameter. Fill them with water, close the cap, and lay them on their sides in full and direct sunlight for a day.

It’s better if you place them on a shiny surface, such as corrugated metal roofing, and angle them towards the sun so that they sun’s rays will strike the bottles more directly. If the water is cloudy or turbid, filter the water with cloth or cotton until it is clear. Keep the bottles in direct sunlight for at least 6 hours. If the sky is cloudy, you will need to keep the bottles out for two days.

So, how does it work? The strong ultraviolet light (UV-A) from the sun not only destroys bacteria directly, but it also reacts with oxygen to create oxygen free-radicals which can also kill bacteria. One way to improve the effectiveness of the process is to aerate the water by shaking it. To do this, fill the bottle 3/4 full, cap it off and shake it. Then fill the bottle up the rest of the way until it’s completely full. This oxygenates the water and increases the amount of oxygen free-radicals created by the sunlight.


This is surely not an exhaustive list of water treatment methods, but I wanted to list some common ones for consideration. Rather than rely solely on one method of water purification, I would consider having many methods in one’s survival arsenal. So goes the preparedness maxim, “two is one and one is none.” This definitely applies to methods and ideas as well.

Do you have any other methods not considered here? What do you think?

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August 20, 2010

M.D. Creekmore [send him mail] is a full-time blogger and preparedness consultant. He currently lives completely off-grid somewhere in the Appalachian mountains and is currently working on his upcoming book The Dirt Cheap Survival Retreat for Paladin Press. To connect with M.D. Creekmore please visit his Survival Blog.