SHTF Water Filtering and Purification For PreppersWhen it comes to SHTF water filtering and purification for preppers we all know the basics and how important it is. Understanding which water filters to get, and how water filters really work can be a little confusing though.

We all know the big names like the life straw, Berkey and my favorite the Sawyer water filter, but do we really understand which filters can do what, and which ones can’t do what we thought they could do? The water filter might say how many microns it is, but do you know what that means to you? If not, you will after you read this article.


Now before we get into how to filter water if we don’t have any of these fancy gadgets like a LifeStraw or a sawyer filter, I want to talk about what makes a good water filter, and give you a better idea about how to pick the water filter that fits your needs.

How Does Water Filtering Work

Filtering takes out the bacteria and parasites like cryptosporidium and giardia, but to understand which filter is going to work the best, we need to know how these water filters work. Let’s start with a regular store bought water filter and then we will go over DIY filters.

Important: Sometimes you see people on these survival shows that can drink straight from a stream and not be affected, this is because they have either built up an immunity like our ancestors, or because of the magic of editing. Most of us drink tap water, bottled water or well water these days and do not have the same immunity…drink at your own risk.

What is a Micron?

Filtering, bacteria and protozoa are measured in microns, to put this in perspective 1 inch = 25,400 microns. How this works is the water is forced through the material in the filter that contains pores .1 or .2 microns in size. If giardia is 8 microns in size, a 7 micron filter or lower should catch it.

A good water filter will state that is “absolute”, meaning that if it says it is an “absolute 1 micron filter” none of the pores in the water filter are larger than 1 micron. If it doesn’t say “absolute” it means the pores are around 1 micron, not less than.

A couple of good bug out bag water filters are the LifeStraw which filter down to about .2 microns, and the Sawyer Mini which is about .1 microns absolute.

This is all great, but how big are the bacteria we are trying to take out right?

How Big is a Microorganism?

Water filtering micron sizesBecause we can’t see these little nasty microorganisms in our water we need to be certain that our water filter is going to do the job we need it to. We all know what happens when you assume something (ASS-U-ME) and in a survival situation it is critical to make correct choices and leave nothing to chance.

Bacteria: These are microorganisms like salmonella and E.coli. These are caused by human and animal waste and are usually found in our food, but can be found in dirty water as well.

Bacteria such as salmonella and E.coli are around .2 to 4 microns in size, meaning most good water filters should take care of these.

Protozoa: These are microorganisms like Giardia and Cryptosporidium. These are also caused by human and animal waste in the water, as a matter of fact most of the pathogens you find in water are caused by animal waste.

Giardia is about 8 to 12 microns in size, and Cryptosporidium is around 4 to 6 microns in size, both well within the range of a good filter.

Viruses: Viruses such as the Entero virus and hepatitis for example are between .004 and .1 micron in size, this means most water filters will not take out viruses. Although water-borne viruses are rare in the North American back country, they might be more prevalent in an urban area, especially during a pandemic.

Important: Most water filters will not remove chemicals, will not filter out heavy metals, and will not desalinate water. It is virtually impossible to remove a chemicals from water regardless what method you use.

How to Choose a Water Filter

There are quite a few differences when it comes to filters and what pathogens they remove, picking the right water filter depends on your needs and your budget. Berkey water filters are great for home use, but if you’re looking for something more portable a Sawyer might be the way to go.

Microns: First and foremost you want to make sure the filter is going to do the job you need it to. Make sure the water filter is the right size in absolute microns to remove protozoa and bacteria.

Lifespan: Some expensive filters will filter up to 1 million gallons, some like the Sawyer Mini will filter 100,000 gallons. A million gallons sounds great right, but if the average person needs 1 gallon of water per day that’s 365 gallons per year. Even if you had a family of 4 it would still take 66 years to drink 100,000 gallons of water.

Budget: All 3 of these are why I love the Sawyer Mini so much, and why I keep mentioning it. It has a .1 micron filter, costs around $20 and will filter 100,000 gallons of water. For this price the Sawyer Mini outdoes any portable water filter.

Water Disinfection Process

As you will see in the chart below, boiling is the best way to clean your drinking water, but remember to filter your water before boiling. Filtering the water first will remove some of the bigger particulates and debris giving you cleaner water.

Boiling: You don’t necessarily need to boil water to kill the pathogens in it…

  • Water at 160° for 30 minutes will kill the pathogens.
  • Above 185° for a few minutes will kill the pathogens in it.
  • Boiling water is 212° and will kill the pathogens as soon as it comes to a rolling boil, although I tend to let it boil for 30 seconds to a minute. This is important because if water is in short supply you don’t want to boil it too long because you’re precious drinking water will evaporate.

Water at sea level has a higher boiling point that water at higher altitudes, have a look at this chart and see where you stand. Here in Colorado we are around 5,000 ft above sea level, so our water boils at 202°.

Water disinfection methods

Bleach: When using bleach to purify your drinking water only use ¼ teaspoon per gallon, or ½ teaspoon for cloudy water and let stand for 30 minutes. You will also need to use bleach to sanitize your water containers for long term storage using this process.

Never use scented bleach to disinfect your drinking water, scented bleach has other chemicles that make it “smell nice” and can be harmful if ingested.

Purification Tablets & Drops: These are Chlorine Dioxide and work better than regular chlorine, although not as cost effective. These are a great addition to your bug out bag because they are small, lightweight and could be a life saver.

I prefer the Aquamira tablets because I have a hard time thinking of “drops” as a measurement, how much is a drop? If I accidentally add too much how do I figure out how much I added? A tablet is much easier, Aquamira tablets are 1 tablet to 1 liter or quart (1 liter = .92 quarts) of water.

Distilling: Although this is time intensive distillation will give you the cleanest water. In most situations this will not be a viable option, unless you have access to a moonshine still that is.

Distillation is basically heating up the water to the point it becomes vapor, cooling that vapor and catching the purified water. This can be done with a pot and a coffee cup (pictured above) or even a solar still that I talk about below.

Water Treatment and Cleaning Chart

The chart below takes everything we just went over and makes it a little easier to understand. This chart shows you how effective certain filtration and disinfection processes are, and how well they work together.  If you need to download this picture just right click it and choose save image as.

Filtering and Disinfection Chart

Here’s how it works…

By using the pathogen removal key on the top right you can see how effective a process is. For instance a 1.0 micron filter is 3 plus’s (high effectiveness) affective against protozoa and bacteria, but if you use a combination of water filtration and disinfection it becomes very high effectiveness.

You can also see the size of the pathogens in microns on the left and it’s important to note that the filter in this example is a 1.0 micron filter. The filter you use such as the Sawyer Mini or the LifeStraw are well below this but are still not affective against most viruses.

DIY Water Filters

The same process holds true for a DIY water filter, other than it is a little more bulky than a store bought water filter. Knowing how to make a water filter could turn out to be very important if you are left in a situation where you have nothing. While these are not as efficient as a store bought water filter, they are far better than nothing.

DIY Water filterLarge Gravel: The top layer of a water filter should be larger objects like rocks or gravel, the only purpose of the first layer is to remove some of the larger debri so it doesn’t clog the filter in the lower sections.

Sand: The second layer should be material that is much smaller in size like sand. This layer will catch even more of the sediment that passed through the first layer of rocks.

Charcoal: A layer of charcoal will take out some of the microorganisms in the water. You can use charcoal from a fire, but only the charcoal, not the ash from the wood. Remember to crush this up as much as you can to give it more surface area to catch the pathogens in the water.

You can also use activated charcoal as well, although you would probably have to purchase this beforehand. Activated charcoal and regular charcoal are almost identical –To create activated charcoal, regular charcoal is heated with a gas that causes the charcoal to expand, creating a porous surface that traps toxins.

Cheese Cloth or Coffee Filter: The last thing you want is for the water to go through your filter just to let everything pass through at the end. Using a coffee filter, bandana or cheesecloth will catch any of the sediment or charcoal from going into your clean drinking water.

Remember though, these filters are not as effective as a store bought filter and will not remove all the pathogens in the water, always boil the water if that is an option before you drink it. If boiling isn’t an option you will need to ask yourself “do I drink this dirty water? Or do I die of dehydration?”

More DIY Water Filtering Options

Rather than explain these in this post I am going to link to some articles and videos from people who have already done it. Just like everything else, it’s always a good idea to have these water filters and survival tools, but we need to have the knowledge to get by if we don’t.

Boiling Water with Rocks: As this article says, this is a little more complicated than you think because it requires having a fire and hollowing out a log. [Read More Here]

Bandana Tripod Filter: Here is an article from the 7P’s blog about building a tripod water filter with materials found in the wilderness.

Water Condensation: Wrapping a tree branch with a plastic bag catches the water from the vegetation, this is called transpiration. The same process can be used by making a solar still.

Bandana: Not only can you use a bandana for a tripod filter, you can wrap bandana around your ankle and walk through the grass early in the morning to collect water. This article from Survival at Home has a few more uses for a bandana.

5 Gallon Bucket Water Filter: I will be trying this one very soon, for now here is a great video showing how to use 2 five gallon buckets with a Berkey replacement filter.

Water filtration and purification for preppers is a little bit different that what the average person would be looking for, most people look for water filters that remove stuff that is unhealthy, we want to remove stuff that can harm us or even kill us. Regardless which filter you use, make sure it’s going to do the job you need it to.



Survival and being prepared should not only be a passion, it should be a lifestyle. The definition of a prepper is "An individual or group that prepares or makes preparations in advance of, or prior to, any change in normal circumstances, without substantial resources from outside sources" Like the Government, police etc. I don't believe that the end of the world will be the "end of the world" I believe it will be the end of the world as we know it now. You can also find me on Google Plus and Twitter

    6 replies to "SHTF Water Filtering and Purification For Preppers"

    • Mark L

      Have you heard, or do you know the water filtration technique using Hydrogen Peroxide?

      • Dale

        I haven’t Mark, but you got me interested. I.m not sure if it would remove waterborne cysts like cryptosporidium but I found this site here:

        • Kathleen O'Meal

          Do you know why we autoclave surgical instruments at higher temps than boiling in the hospital? This is one reason I always recommend pressure cooking at 15 pounds over boiling alone. It is one thing to deactivate a bug when it is in a petrie dish, so to speak, and quite another to kill the bug when it is hiding out in particulate. Moreover, for example; I can envision some evil piece of crap or many in unison, injecting C. Bot. spores into public water lines unseen, in the night….by the time it is discovered…many will be dead or permanently handicapped. We need to understand how to make water safe…..good article

    • Andrew Reinhold

      Is it possible to fill large buckets with water and leave it for months-years and then purify it when the water is needed? is this possible? if so how would this be done?

    • Kathrin Diaz

      I must say that this review is comprehensive. I have learned further about water filters. Now I have to be more keen in choosing the right water filters for my family. Thanks a lot!

    • Barry

      The detail you went into for filtering was spot on, however have you heard about adding himalayan salt afterwards. I know it’s not going to taste good but its suppose to help you body absorb minerals better.

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