Water Purification Techniques


Considering that we can only survive an average of three days without clean water, having that water is an extremely high survival priority. But the key here is that it has to be clean water. During a survival scenario you can’t count on any water being clean, even your normal water sources. All water that you are going to drink has to be purified, because you can’t afford to have the water give you dysentery.

Let me be clear about what I’m talking about here. When I use the term “clean water” I’m not necessarily talking about water that is clear of any sediment. Water can be clear and still dangerous to drink. Likewise, water can look cloudy and still be safe to drink. It’s not whether or not there’s anything in the water that I’m concerned about, it’s what is in the water. Specifically, I’m talking about water that is free of microscopic pathogens.

Naturally occurring water, other than rainwater, is usually teeming with bacteria, protozoa and other microscopic organisms. It can even have viruses in it, although that is not as common. It is these microscopic pathogens which are the big danger that we need to avoid, as they can make us sick or even kill us. In most cases, they cause diarrhea and vomiting, which can kill us through dehydration.

But that doesn’t mean that rainwater is clean either. While it is clean while falling to your roof, once it gets there, it is contaminated by bird droppings on the roof, so it must be treated as dirty water and purified.

Granted, these pathogens aren’t the only things that can be dangerous in the water, chemicals and heavy minerals can be a big problem too. But they are the biggest risk, except in those rare circumstances where there has been a chemical spill. If that is the case, you’ll probably hear about it.

There are several different ways of purifying water that we can use. Most are fairly easy. Because this is such an important area of survival, you should keep several of them available to you.


Filtration is one of the most common means of water purification; so common, that our municipal water authorities use it for both fresh water and waste water treatment. Gross filtration can remove sediment and particles from the water, but for those microscopic pathogens, we need really fine filtration.

Most home water filters, such as whole house filters and faucet filters don’t do more than remove sediment. They’re typically rated at 5 or 10 microns. But bacteria are 0.5 to 5.0 microns in length. Viruses, which are much smaller, are 0.02 to 0.25 microns. We need much better filters to remove those from the water. Fortunately, such filters do exist.

Most preppers buy two different types of water filtration systems; one for home and one to put in their bug out bag. The home one needs to be more robust, with a greater capacity. On the other hand, the one for the bug out bag needs to be compact and lightweight, while still doing a good job.

There are many different water filters on the market to choose from. Two of the best are the Berkey and the Sawyer. The Berkey uses a multi-layer filter cartridge, which can remove more than any other commercially available filter on the market. While expensive to buy, the Berkey is one of the cheapest to operate, as the filter cartridges last for a 3,000 gallons each. The Sawyer lasts even longer, because it is a hollow fiber membrane that is back-flushable. While it won’t remove everything the Berkey will, their larger filter will remove both bacteria and viruses, and is rated as being good for a million gallons.

The Bio Filter

If you don’t have a water filter available, a good one can be made out of gravel, sand and activated carbon. This system is called a bio filter, and was originally developed for people in third-world countries, where water purification is rarely available. The bio filter works similar to our water treatment plants, but is small enough for a family to use.

You can either use one five-gallon bucket, layering the materials or three buckets, stacking them one on top of the other, with one material in each bucket. In this case, you will need a water outlet in the bottom of the top two buckets, with a hole in the lid of the bucket below for the water to come in. That outlet should be screened over, to keep the filter medium from passing from one bucket to the next along with the water. The bottom bucket needs an outlet too, for the clean water to come out.

The top bucket should have 25 lbs. of pea gravel in it, the middle one 25 lbs. of sand and the bottom one 25 lbs. of activated carbon. Be sure to rinse each of those filter mediums thoroughly to remove dust and silt from them. Water entering the top will have larger particulates removed by the gravel, smaller ones by the sand and the activated carbon will remove most of the bacteria.

Some people teach using five layers, making it: gravel, sand, activated carbon, sand, gravel. But that is not necessary. The additional layers of sand and gravel don’t do anything in that case, other than taking up room that can be used for more activated carbon.

Chemical Purification

The other really common means of purification is chemical purification. The same water treatment plants that filter our drinking water also chemically treat it to kill any microscopic pathogens that are not filtered out. The most common chemical they use for this is chlorine.

Chlorine is a very convenient for us to use as a purifying agent because we can buy it in the form of household bleach. The major brands of bleach are six percent chlorine, making them perfect. If you buy an off-brand, just be sure to check that it is also 6%. If it is, it’s just fine to use.

To use bleach for purifying water, add 8 drops of bleach per gallon of water and mix well. Allow the water to sit for 20 minutes and it will be safe to drink. If you don’t like your water smelling of chlorine, allow it to sit overnight and the chlorine will evaporate out of it.

According to the EPA you can also use “pool shock” for swimming pools to purify water. To do this, start by dissolving one level teaspoon of pool shock in one gallon of water. This will produce a chlorine solution which can be used for purifying water. You will need to use 2/3 oz. of this solution per gallon of water, mixing it in and allowing it to sit for 20 minutes, like the chlorine bleach.

Tincture of iodine can also be used to purify water in much the same way, the only difference is the quantity of purifier needed. However, iodine is considerably more expensive than chlorine bleach. For clear water, use 10 drops of iodine and for murky water use 20 drops.

Heat Purification

The third method of purifying water is through heat. It’s pretty common knowledge that water can be purified by boiling it; but what most people don’t realize is that the water’s temperature doesn’t have to be raised all the way up to boiling to purify it. Water boils at 212°F or 100°C, but the microscopic pathogens we are concerned about die in 15 seconds at 162°F (72°C). As an alternate to that, they will die at 145°F (63°C) if that temperature is maintained for 30 minutes. This is called “pasteurization.”

There is a device called a WAPI (water pasteurization indicator) which was developed for use in third-world countries. It consists of a wax pellet in a plastic capsule. When placed in water that is being heated, the wax will melt at 162°F, informing you that the water is pasteurized. Once removed from the water, the wax pellet hardens again, allowing the WAPI to be reused over and over again.

Obviously, you have to have heat to boil water or even pasteurize it. Most people do this over a fire. For that reason, it’s a good idea to have an aluminum or stainless steel water bottle in your bug out bag or survival kit, rather than a plastic one. At home, you’ll probably have pots you can use and a fire pit or wood-burning stove for cooking, which can also be used for purifying water.

But that isn’t your only option. People in third-world countries will fill used plastic soda bottles with water and place them on their corrugated metal roofs. The sun beating down on those roofs is enough to heat the water to the point of pasteurizing it. A WAPI in one of the bottles lets them know when they have been on the roof long enough.

Distilling Water

The absolute best method to purify water is to use a still to distill it. This process involves heating the water to the point where it turns into steam and then condensing the steam back down to liquid. In the process, everything gets left behind, making this the best method for use in removing not only microscopic pathogens, but also chemicals, minerals and even radioactivity.

The problem with distillation is that it is equipment and labor intensive; you have to build a still and keep a fire going to heat it. The still consists of a sealed container where the water is heated, like a pressure cooker or pressure canner. A copper tube is attached at the steam outlet, allowing the steam to escape into the tube. Copper is used because it is one of the best heat conductors there is, ensuring that the water vapor condenses back down to water.

The tubing must run downhill the whole way, once it clears the pot, so that the water will run out. That’s usually accomplished by making a coil out of it, spiraling downwards, with the water dripping out the end, into some sort of container.

A solar oven can be used as a still as well, as water put into it will evaporate quickly and rise to hit the glass cover on the solar oven. That water will then run down the glass, where it can be captured and collected. This is a slow way of purifying water, but it will work, providing very clean water.