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Water Filtration vs Purification: A Basic How-To

Next to air, water is what we need most. In a challenging situation, it is critical to be able to find, store or treat water. Our bodies are about 80% liquids. We lose water in three ways: perspiration, breathing and urination. Dehydration of 6 to 8% of the body’s weight results in decreased body efficiency. In the summer heat, we lose about one gallon of water per day. Within three days of water depletion or loss, the body and organs can experience severe damage. Blood loses its density; heart attack and stroke possibilities increase; the kidneys begin to fail; the brain begins to hallucinate.

Bubbles breaking the surface of water

Not only is drinkable water essential to maintaining health, it is also important for cooking, personal hygiene, sanitation, cleaning wounds, sprouting seeds and reconstituting dehydrated foods including baby formula. Because water is so essential for survival, it is wise to have both a stored supply of drinking water and a way to acquire water for your continuing needs.


In order to understand how to make water potable (suitable for drinking), we must first understand what things make water unsuitable for drinking. Most surface water (rivers, lakes, streams, reservoirs) contains some types of microorganisms (protozoa, bacteria, viruses) and/or pollutants (chemicals, foul odors, sewage, spilt fuel).

Microorganisms are living microscopic cells that, when consumed, can cause diseases such as dysentery, cholera, typhoid and hepatitis. Some microorganisms can even cause death for those with weak immune systems (children, elderly, sick).

Protozoa (the largest of all microorganisms) include such parasites as Giaridia Lamblia and cryptosporidium. Bacteria (medium-size microorganisms) include E. coli, Vibrio Cholerae, campylobacter, and salmonella, all of which are found in human and animal waste. The most common occurrences are in preparing and processing food at home and in the food industry (especially associated with not washing hands after using the bathroom). Viruses are the smallest of all the microorganisms. They include hepatitis A and E, Norwalk virus, rotavirus, poliovirus and echovirus.

Pollutants generally fall into two categories: man-made and natural. They include water contaminants such as minerals (salts) and heavy metals. Man-made pollutants are introduced into water sources by manufacturing plants, poor waste and disposal management, air pollution, and so on. Most often these pollutants are chemicals, fuels, sewage, or their by-products. These pollutants can cause water to taste foul, and they can cause physical ailments or death.

For a long-term emergency plan you need to have a method to make questionable water "potable" and safe. You should also have a method of replenishing your drinking water. There are three primary methods to convert "raw" undrinkable water into safe "potable" drinking water: purification, filtration, and stilling (solar). Each method has its advantages and disadvantages. NOTE: Start with the cleanest, salt-free, and least polluted water in your surrounding living area. Cold river water that is running is preferred over warm stationary water. Realize that no method is perfect and sometimes combining methods is the best solution.

There are three general ways to make surface water free from disease-causing microorganisms: A) add extreme heat to the water (boiling and distilling), B) add disinfectant ( purification, chemical or silver), and C) add light (ultraviolet).

Historically, boiling water has been the main way to disinfect water from microorganisms because it kills them all if done correctly. Recommendations are to boil water for at least three minutes to kill all viruses. Bacteria and protozoa are dead at the first bubbles. But there are drawbacks to boiling water. First, boiling can require a lot of fuel and cooking equipment. Second, you must consider the long cool-down period. Third, some of the water will evaporate before it is ready to drink. Fourth, the water will still have particulate substances in it, so you should use a clean handkerchief to filter it before drinking. Last, boiling water does not eliminate pollutants, poor taste or foul odors. In fact, boiling can give water a stale taste. A helpful hint to improve the taste is to transfer water from one container to another several times while boiling.

Two primary chemicals are used for purifying water: iodine and chlorine. These two chemicals are lightweight, low-cost and relatively easy to use.

Iodine has been found to be very effective against viruses, bacteria, and protozoa with the exception of cryptosporidium. Using iodine has some drawbacks. The colder the water you wish to disinfect, the more required time is needed for disinfecting. Because iodine is absorbed into dirt and debris, which is found in water, its purification dosage varies. Pregnant women and people with thyroid conditions should not drink water purified with iodine. Additionally, iodine is a short-term water-purification solution and should not be used regularly for more than three months. Iodine does not change the clarity of water but it does change its taste. Iodine is not necessarily a flavor that people enjoy. This taste can be improved by adding a sugar-based drink/juice mix. A good product is Potable Aqua™ Iodine Purification Tablets—Just add two tablets per liter of water.


Chlorine bleach can also be used to purify water. The Federal Emergency Management Agency (FEMA), the Clorox® Company and the Red Cross have recommended using Clorox Bleach to purify raw water. Their pamphlet states, “…use regular household bleach that contains 5.25% sodium hypochlorite. Do not use scented bleaches, color safe bleaches or bleaches with added cleaners.” When using bleach to purify, “add 8 drops of bleach per gallon of water, stir and let stand for 30 minutes. If the water does not have a slight bleach odor, repeat the dosage and let stand another 15 minutes.” The process of chlorination will cause dirt and debris to settle to the bottom of the water container and make the water visually clearer. There are some drawbacks to the chlorination method. If the household bleach is over six months old, it may not have enough potency to disinfect. You must be very careful if you attempt to use household bleach as a purifier. Chlorine is very poisonous and adding too much can cause illness, internal organ damage or even death. If you decide to use bleach, be sure to add it at the time you intend to use your water, NOT when you store it.


Because ultraviolet light requires electricity, it is mainly used as a home filtration method for water; it is not typically practical otherwise. Water enters an ultraviolet-lighted chamber and swirls around a high output, low-pressure mercury vapor lamp, which emits powerful ultraviolet light. The energy components of microorganisms absorb the light energy, which disrupts their DNA preventing them from reproducing. UV lighting literally sterilizes the microorganisms rendering them ineffective in making one sick. UV lighting adds no chemicals to change water’s taste. Beyond requiring electricity, UV methods demand some form of filtration to remove dirt, debris, chemicals, tastes and odors. UV purification is considered a good “stage” of the purification process, but it is not complete by itself.



Water filtration simply means to strain out the impurities from a water source. The larger the impurity particulate the easier it is to filter. The opposite is true also, the smaller the impurity particulate, the harder it is to remove. Thus, the size of the filter pore and the durability of the filtering element are important to the filter’s longevity and ability to perform. Most filtering elements are made of ceramic, glass fiber, hard-block carbon, or materials that resemble compressed surgical paper.

Ceramic elements (most expensive, most durable, and maintainable) have the smallest pore size (0.1-0.5 microns) and are used by some of the leading portable water filtering companies in the world. Portable ceramic filters boast an impressive list of long-term users, such as: International Red Cross, World Health Organization, Armed Forces (USA, Germany, Portugal, Switzerland, and US Navy Seals), United Nations, and the FBI. Ceramic elements can filter only free floating particulates and microorganisms. They do not remove chemicals, poor tastes, odors, or pollutants.

Glass fiber elements and compressed surgical paper (mildly expensive, medium durability, and usually not cleanable) also have small pores (0.2-1.0 microns). Like the ceramic filter, they remove only particulates and microorganisms, but they do not help much with pollutants. These are good low-cost filtering elements for home, backpacking and scouting needs, but they are not good for long-term storage because they can develop mold and mildew and they are hard to clean.

Hard-block carbon elements (less expensive, brittle, and not cleanable) have a small, but still effective pore size (0.4-2.0 microns). They are also used as an absorption filter. The best contribution that carbon makes to filtering is its ability to reduce chemical quantities, poor taste, odors and many pollutants. Because carbon is only mildly effective in filtering out particulates and microorganisms, it is mostly used as a second or third stage filter in home and portable water use. It is seldom used as a stand-alone filtering unit.


Solar stills operate upon the "greenhouse effect." A clear plastic barrier (a plastic bag, ground cloth, or a plastic grocery sack) is placed over a “source,” such as the ground, tree branches or other organic materials. The sun’s (solar) energy passes through the barrier and heats the source material. Moisture from the source vaporizes, rises and then condenses on the underside of the plastic barrier. The moisture is then collected as drinkable water. Solar stills are capable of distilling almost any tainted water, even seawater. Solar stills can condense drinkable water from substantially anything that contains moisture. The only source materials that it cannot distill drinkable water are materials that give off toxins, such as fluids with high amounts of chemicals, radiator fluids, and fuels.

Solar stills are easy to assemble and require only two essential components: 1) a container to catch the water, and 2) a large sheet of clear plastic (from 6’ x 6’ to 9’x 9’). Optional items include a long plastic drinking tube with end cap, a small shovel, and duct tape.

Solar stills are inexpensive to make and most of their component parts can be purchased at a hardware store. However, solar stills should not be your only method for finding drinkable water during an emergency. This distilling process is extremely slow and only small amounts can be collected daily. A solar still is good when you have exhausted other methods.


Combining methods can make water safe to drink and taste better. Become aware of your area’s surrounding surface water and determine what methods work best to make that water safe to drink. Educate yourself to know what works, what doesn’t, and how you could get more drinkable water if needed.

We hope this information has proved to be valuable. The time to store water is now. The water that we take for granted becomes absolutely critical in an emergency. Water is not an item you can afford to overlook in your preparedness program.


Editor's Note (3/26/2014): The Hydropack is another method that can be used to filter and purify water.

The Hydropack has .05 micron (5 angstrom) sized holes for water to pass through when dropped into a water source. Simply drop the Hydropack into your water source and let it absorb the water, filtering out chemicals and other contaminants to create an electrolyte drink much like a sports drink. However, there could also be situations when the pollutant in the water is small enough that the Hydropack won’t solve the issue.


Vicki Tate is the co-author of the book Cookin’ with Home Storage and Designing a Livable Food and Water Storage (an audio cassette).
Barry Crockett is the author of the book A Year's Supply, How to Assemble a 72-hour Emergency Kit and Diaster Action Guide.

19 thoughts on “Water Filtration vs Purification: A Basic How-To”

  • Margo

    I wish there was an article written to help those of us city dwellers in apartments to know the best way to FILTER water in an extended emergency. Storing large quantities of water is not feasible, but I'm looking to do 5 gallons at a time in a fairly short period of time. I would love to have a comparison of filters, an explanation or micron sizes and what can get through at each micron level (for example: does .5 microns allow certain deadly bacteria to pass through that .3 will eliminate? etc). I am not wealthy. I need to make the right decision the FIRST time I buy!!!

    • beprepared

      Great questions. We'll put something together to walk you through all of that information. Thanks for your input!

  • Sylvia

    Can a spiqot be inserted near the bottom of the barrel?

    • beprepared

      Hi Sylvia! a spigot cannot be attached at the bottom of our 55-gallon (or larger barrels). If you would like to use a spigot to get your water out more easily, you might want to consider checking out our aqua pak or aqua tainer (http://beprepared.com/catalogsearch/result/?q=aqua+pak). These are smaller water storage containers that come with a spigot attached at the top. You can also siphon water from your barrel into a 5-gallon jug (http://beprepared.com/reliance-5-gallon-collapsible-fold-a-carrier.html). You can purchase a spigot (http://beprepared.com/catalogsearch/result/?q=spigot) to attach to 5-gallon jugs as well. Hope this helps!

  • Howard Collier

    A most Excellent presentation about water filtration. Superior information is presented here. Thanks kindly.

  • Tim

    You did not mention RO style systems. Such as the hydropak. I understand it is an entirely different means to purify water and would appreciate your input.

  • Denise Souligney
    Denise Souligney March 19, 2014 at 6:19 pm

    I've been saving heavy duty 1 gal. containers for about a year. I soak them for days in anti-bacterial dish soap. I then fill them with tap water and store in a cool dark place. What should I do in case of an emergency to make it safe? Please help

    • beprepared

      First off, what is the recycling number of the gal. containers you're using to store your water? CAUTION: It is recommended NOT to store water in Milk jugs because it is unsafe. If it's not a milk jug, you can find the number of your container by flipping it over and looking for a triangle with a number in the center of it. If the number is 1, 2, or 4, this means that this type of container is safe to store water in. These numbers are BPA free and less likely to contaminate your water. Plastics generally absorb flavors and those flavors may get into your water. Even if you do wash the container with anti-bacterial soap, that washing will not kill microorganisms in the water. To do this, you'll need to purify your water using something like our micropur tablets To ensure the safety of your water, you have to have a proper container for water storage, and purification supplies, but also Rotation is key. You'll want to set up a rotation system for your water, maybe every 3 months, to make sure the water is safe and clean to drink.

  • vickie cloud

    where I live in west texas we dont have good water..and what we have is bad...so we buy the water bottles which is getting to be a pain in the neck...we live in an apartment and want to know what kind of water purification to use...the taste of the water is soo bad...I would love to drink water out of our sink...I think we need some kind of water purification for apartments and bathrooms etc...something portable...

    • beprepared

      Hi Vickie,
      Great question. Check out our article, "Find the Right Water Filtration System for You" at this link http://beprepared.com/insight/12130/find-the-right-water-filtration-system-for-you/?&sc=BLOG&oc=BP0001B1074 to get an initial idea of what type of filter would work best for you and your family. You could also try one of the following options for purifying your water: If you want to drink from the sink, you could get a Katadyn Combi filter and purchase the Combi Faucet adapter. It will cost you a bit, but would be worth if for the amount of use you will get out of it. This filter comes with activated carbon which helps to make the water taste better. Another thing you can do is store water (similar concept to getting the water bottles, but with less hassel). Since you live in an apartment, you'll want to probably get some type of stackable water storage containers that are smaller than, say a 55 gallon barrel. Check out our Aqua Pak and Aqua Tainers. They store 5-10 gallons of water and you can stack them safely. With this type of water storage, you'll want to use micropur tablets to purify the water.

  • Greg Malone

    We have county water and the taste is horrible. I was buying bottles water and using a pitcher filter for a few years but it was expensive and the filter only did so much. I had a Berkey gravity filter similar to the Katadyn for just in case but I starting using it full time about two years ago. It is awesome and I save a bundle in bottled water by refilling my own containers. It was an investment but I would venture it has paid for itself a couple of times over with great results for us.

  • EastTenn

    Boiling water will remove certain chemicals such as methanol. Xylene, will form an azetrope with water and boil around 95C so it to may go.
    Another helpfull thing to do if posible would be to build a decanter. Debris such as dirt would fall to the bottem, chemicals such as oil that are lighter than water would float, and chemical that are heavier would be below. However, chemicals such as methanol will not seperate out of water. That is where the boiling comes in.
    If you boiled the water in an open container for a while then boiled the water to another container, the vast majority of polutants would be gone.
    If you are curious, I am a chemical operator that runs several distilation columns.

    • beprepared

      Thanks for your comment. I am curious though: What is a decanter? And how does it work to clean your water?

  • Acct4it

    In light of the Flint, Michigan water with LEAD in it from a river, what can a family do to purify their water in this instance and is there a way to test for harmful substances like lead in water so you know how to treat it?

  • Carol Ann Shepherd
    Carol Ann Shepherd July 6, 2016 at 1:34 am

    I highly recommend the Berkey filtration system. You can purchase these Berkeys in several sizes. I suggest the largest so you don't have to refill as often. They are portable and travel easily. I have had mine for 5 years and could not live a day without purifying my water. It extracts 99.9% of contaminants and the filters are cleanable. The investment is worth every penny. See the Berkey Guy. Lifetime guaranteed.

  • Dhenard

    I have a couple of suggestions to help with water filtration. This comes from being a chemical operator with 9 years of experience in distillation. The first thing I would do is build a decanter. Dirt and any thing else heavier than water will sink to the bottom. Lighter fluids such as gas and oil will create a film on top of the water. If possible, install a drain in the water so you drain the water in between. If not scoop the top film out. The next to do is boil the water. Remember, chemicals such as methanol will not separate out of the water and they have a lower boiling point so boiling the water will remove it from the water. Other chemicals such as xylene and gasoline will separate out the water in the decanter. After you boil the water for a few minutes to remove the low boilers from the water, you can then try to boil the rest of the water into a another container leaving high boilers such as salt in the container. Hope this helps

  • Larry

    I have a pool with 10000 gal. of potential drinking water. Since pool water has chemicals,How would you treat pool water so it is safe to drink?

  • Tonia

    In your article under chlorine bleach. "Their pamphlet states, “…use regular household bleach that contains 5.25% sodium hypochlorite". According to the phone call I made to CLOROX, this percentage of bleach is no longer manufactured. Only CLOROX Concentrate which is 8.3% Sodium Hypoclorite. Any comments on this issue. All information I have found, Government or otherwise, is based on 5.25%. I don't know the amount at which poisoning would occur, but I thought this might be important to consider.

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