Making Water Safe to Drink: 7 Disinfection Techniques

Safe drinking water is absolutely essential for survival. In the event of a disaster, our clean, safe drinking water supply may be suddenly disrupted. Have you considered how you are going to make your water safe to drink?

Water can be made safe to drink by using the following disinfection techniques:

  1. Boiling – heating water to 212 degrees
  2. Pasteurization – heating water to 149 degrees for 6 minutes
  3. Distillation – vaporizing water and allowing it to condense back into a liquid
  4. Chlorination – using chlorine
  5. Iodization – using iodine
  6. Solar Disinfection (SODIS) – exposing water to the sun in a transparent container
  7. Filtration – filtering contaminants out of water

Each of these disinfection techniques has benefits as well as limitations. These methods all deactivate biological contaminants, but only distillation and filtration are able to remove chemical pollutants.

In this post, we will explore the pros and cons of each water disinfection method and learn exactly how to take water from a contaminated source and make it safe to drink.

Why is Safe Drinking Water Important?

Contaminated drinking water is frequently attributed to taking more lives following a disaster than the initial event. Drinking contaminated water can result in serious illnesses such as dengue fever, gastroenteritis, cholera, typhoid, hepatitis, and dysentery to name a few.

Depending on environmental factors, you can survive less than 3 days without water. As little as one day without water may result in dehydration. The symptoms of dehydration can manifest quickly and are dangerous. Dehydration causes the blood to thicken, blood pressure to increase, the risk of heart attack and stroke to increase, kidneys to fail, muscles to lose their elasticity, senses to become dulled, and the brain to hallucinate.

Symptoms of dehydration may include; headache, extreme thirst, dry mouth, little or no urine output, dark urine, sleepiness, fatigue, feeling dizzy or lightheaded, or any combination of these symptoms.

Now that we have established why safe drinking water is a critical component in your preparedness plan, let’s get to work making your contaminated water safe to drink.

What are the Dangers in Contaminated Water?

Exactly what is it that might be lurking in the water that is of concern? We classify the contaminants into 2 general categories: biological and chemical. Purifying water requires both deactivating pathogens through disinfection and physically removing chemical contaminants.

Biological Dangers in Water

Biological dangers in the water are microscopic organisms that are too small to be seen by the naked eye namely; protozoa, bacteria, and viruses. We refer to these dangerous critters as biobugs.


Protozoa are the largest of the microorganisms (2 to 50 microns in diameter). Giardia, Cryptosporidium, microsporidium, toxoplasma, and cylclospora are examples of protozoa.

These parasites can be resistant to chlorine and iodine disinfection due to the protection of a thick outer wall. However, protozoa are easy to filter out because of their larger size. Cryptosporidium is one of the most frequent causes of waterborne illness in the United States.


Bacteria are medium-sized microorganisms (range in size from 1-10 microns long and 0.2-1 micron wide). E. coli, cholera, campylobacter, and salmonella are examples of bacterial contaminants in our water. Most of these little creatures are large enough to be filtered out using a high-quality water filter.


Viruses are tiny (0.004 to 0.1 micron in diameter) and may float right through most filtering systems. They must be deactivated using other methods. Hepatitis A and E, Norwalk virus, rotavirus, poliovirus, and echovirus are examples of viruses which can cause waterborne illnesses.

These organisms are alive and disinfection does not physically remove them from the water. Disinfection methods deactivate or kill the viruses, which prevents them from being able to multiply inside of you and cause illness.

Chemical and Radiation Contaminants in Water

Chemical contaminants cannot be deactivated through any form of disinfection as they are not living organisms. They must be physically removed from the water through filtering or distillation.

The removal method depends upon the individual chemical that has contaminated your water. Examples of chemical contaminants could be; heavy metals, salts, pesticides, fuels, pollutants, and other chemicals.

Nuclear Contaminants

In the event of a nuclear incident, water supplies may become contaminated with dissolved radioactive elements or compounds, and fallout particles. They cannot be removed from water by boiling or chemical disinfection. Settling and filtering is the safest way to remove radioactive elements from the water. Water may also still need to be disinfected to remove any biological dangers that may be present. There are special filters that are designed to remove radioactive contaminants.

Water that has been exposed to radioactive fallout is not necessarily radioactive. Most of the radioactive fallout particles can be filtered out and the water safely used. The first few weeks after exposure to radioactive fallout are the most dangerous. Radioactive iodine particles decay rapidly and contaminated water will become safer over time.

Water barrels may have a layer of fallout on top of them and still be safe to drink. Clean off the dust particles before opening the container to prevent fallout from contaminating the water.

Drinking Water Storage

Stored drinking water is always going to be your safest source of water. Advanced preparation can help ensure you have safe drinking water ready to go when you need it. Visit How to Store Water for Emergency Preparedness for tips on storing water in your own home.

Best Practices for Water Purification and Disinfection

Water purification is the process of removing undesirable chemicals, and biological contaminants, along with particles (leaves, dirt, and such) to make water safe and pleasant to drink. It involves 3 basic steps; clarification, disinfection, and filtration.

Each step is important to achieving safe, clean drinking water. One step may not be necessary depending on the water source. For instance; if the source is a contaminated municipal water supply, you may not need to clarify the water. A “boil order” is commonly issued when the water supply is contaminated. The water has already been clarified at the source, you need to disinfect the water to kill any living bacteria, viruses, or protozoa that may be in the water.

We will review each of the steps to purify water in detail.

Step #1 – Clarification

Clarification removes floating or suspended particulate matter. Think of it as making the water clear.

In this step, water is poured through coffee filters, layers of paper towels, tightly woven cloth or anything that will remove the big stuff you can see. Nature clarifies water as it passes through a porous medium such as layers of sand or soil.

Water can also be clarified by allowing it to settle. The heavy particles (dirt, silt, rocks) will settle to the bottom. Lighter twigs, leaves, and bugs will float to the top. The water is clarified by skimming off the floating particles, then gently pouring the clear water into a clean container. Do not allow the sediment on the bottom to flow into the new container.

It is critical to clarify water before disinfecting because biobugs can hide in the particles during disinfection. Water must be clarified in order for optimal disinfection to occur.

Note: It is possible to use a commercial filter to clarify water. The problem is that all of the particles will shorten the life of the filter by plugging it up. It is best to clarify water before running it through your filter.

Step #2 – Disinfection

Disinfection is the second step in purifying drinking water. It is the process of killing or deactivating microscopic critters that cause illness and death. There are a variety of methods, but not all methods kill all harmful pathogens. Water can be disinfected using these techniques.


The safest method to disinfect water is boiling. When a municipal water supply becomes contaminated, a “boil order” is often issued and residents are encouraged to boil their water before drinking.

Bacteria, viruses, and parasites cannot survive a temperature of 212 degrees. A rolling boil at sea level is 212 degrees Fahrenheit. Each 500-foot increase in altitude causes a drop of one degree in the boiling point. This means at 5,000 feet, water boils at 202 degrees. Higher elevations will require longer boiling times to ensure all the biobugs are destroyed.

Boiling will not remove most chemical contaminants such as heavy metals, salts, and chemicals. Be sure to clarify water prior to boiling to ensure that disinfection is successful. The disadvantage of boiling water as a disinfection technique is that it can be fuel intensive and the water must be allowed to cool before consumption.


A less fuel-intensive method than boiling is pasteurization. However, it is just as effective as boiling. In order for water to be pasteurized, the water must be heated to 149 degrees (65 degrees Celsius) for 6 minutes. A higher temperature will reduce the required exposure time.

Pasteurization can be achieved using a solar oven or traditional heat sources. According to a study performed by David Ciochetti in 1983, “heating water to 66 degrees C (150.8 degrees F) in a solar cooker will provide enough heat to pasteurize the water and kill all disease-causing microbes”.

An effective tool for ensuring water has been pasteurized is a water pasteurization indicator (WAPI). This tiny, reusable device is made from a tube filled with wax which melts and drops to the bottom of the tube when the water has been safely pasteurized. Pasteurization will not remove contaminants such as heavy metals, salts, and chemicals, but it will kill all pathogens in water.


The distillation process is simple but highly fuel intensive. The contaminated water is heated to the point of boiling and the steam is vaporized. The other substances (salt, minerals, heavy metals, etc.) remain in a solid state in the boiler.

The steam is directed into a cooler, where it condenses back into liquid form. All of the impurities are left behind.

While other methods of disinfection only kill the microbes in the water, distillation will kill them as well as physically remove the biological pathogens along with heavy metals, salts, poisons, and most other chemicals. Distillation will not remove substances that have a lower boiling point than water such as oil, petroleum, or alcohol.

Water distillers can be purchased in electric or non-electric models. Solar water distillers (solar still) are an effective way to distill water without using large amounts of fuel.


Chlorine is a popular method of chemical disinfection used in many municipal water supplies. Some protozoa such as Giardia and Cryptosporidium are resistant to chlorine due to a protective outer shell.

Due to that limitation, chlorine should be used to disinfect in conjunction with a high-quality filter. The filter will remove the large protozoa while the chlorine kills the viruses which many filters are unable to remove because they are tiny.

The goal for water disinfection is 1 ppm (parts per million) of residual chlorine. That means that after the army of chlorine soldiers has killed all the bugs there should be one part per million chlorine soldiers still hanging around.

Knowing exactly how much chlorine to use is difficult to calculate because the amount of chlorine needed depends on the number of critters in the water. Chlorine is actually used up in the battle. Too much residual chlorine is bad, too little will leave some critters in the water to make you sick. The safer your water source, the less chlorine you need.

The EPA set 4 ppm as the “maximum residual disinfectant level (MRDL).” Drinking water with high concentrations of chlorine may result in stomach discomfort and other negative side effects. Pool test strips can give you an idea of the amount of free chlorine in your water. Do not drink water with over 4 ppm without running it through a quality filter to remove the chlorine.

Chlorine Dioxide

Available in tablet or liquid form chlorine dioxide works a little differently than regular chlorine. Chlorine Dioxide works through an oxidation process, not by chlorination. The procedure requires a much longer contact time of 4 hours, as compared to 30 minutes for chlorine.

Follow the instructions listed on the package carefully. Chlorine dioxide tablets have a shelf life of 4 years when properly stored. These tablets may improve the taste of the water.

Household Bleach – Sodium Hypochlorite

Household bleach, such as Clorox, may be used to disinfect water. Use only varieties that are free from soaps, scents, thickeners or phosphates. The label should read 5.26 to 6 percent sodium hypochlorite.

Chlorine in the bleach has a relatively short shelf life of 6 months and loses potency over time rendering it ineffective for water disinfection. Be sure to rotate chlorine bleach frequently to ensure adequate strength for water disinfection

The American Red Cross recommends adding 8 drops of bleach per gallon of water. Add liquid bleach directly to clarified water and allow the water to stand for 30 minutes. The water should still smell slightly of chlorine. The residual is referred to as free chlorine. It means that enough chlorine was added to kill all of the bugs with some left over. If you cannot smell chlorine after 30 minutes of contact time, repeat the process and wait an additional 30 minutes.

You can reduce the chlorine taste and smell by allowing the water to sit out in an open container or by pouring the water back and forth between two containers several times. This allows the chlorine to dissipate after it has done its job.

The best way to remove the chlorine taste is to run it through an active charcoal carbon filter. Berkey and AquaRain are both gravity filters that are rated to remove chlorine.

The table below is a quick reference from Clorox Consumer Services for using their products for water disinfection.

Dry Calcium Hypochlorite

Powdered or granulated chlorine, such as calcium hypochlorite, has up to a 10-year shelf life if stored in a cool, dark place. Check out our post Disinfecting Water Using Calcium Hypochlorite for details.

Be careful where you store it. It is a hazardous chemical that can cause chemical burns to the skin, eyes and mucous membranes. Take precautions by wearing gloves and protective eyewear when handling.

The amount of available chlorine is important. Calcium hypochlorite can be purchased in different concentrations. Purchase a brand that has at least 68 percent available chlorine.

The Departments of the Army, Navy and Air Force released a publication entitled, Sanitary Control and Surveillance of Field Water Supplies, on 1 May 2010 (Page 70) where they set standards for use of calcium hypochlorite for water disinfection in the military (U.S. Army Center for Health Promotion and Preventive Medicine 2003).

The calculations to create a stock solution from dry calcium hypochlorite in the table below are taken from those military standards.

The standard calculation for a 5 percent stock solution is based on dissolving 1 and 1/2 teaspoons of 68-70 percent dry calcium hypochlorite in 1 cup of water.

Liquid chlorine is volatile and weakens in strength over a short period of time. Dry calcium hypochlorite is stable and can be stored for many years. Making up small, fresh batches of homemade liquid chlorine bleach will ensure its effectiveness for deactivating pathogens in drinking water.

The stock solution in the table above can be used to disinfect water following the same directions provided for liquid household bleach. When using the stock solution to disinfect drinking water, the military standard recommends mixing and allowing water to stand for a minimum of 30 minutes to ensure adequate disinfection time prior to consumption. Extremely cold water may require additional chlorine or longer contact time to deactivate pathogens in the water.

Dry calcium hypochlorite can be used to disinfect a 55-gallon barrel of water. Fill the barrel with at least 50 gallons of clarified water. Add 1/4 teaspoon of dry bleach powder, and 1/2 teaspoon if the water is cloudy. Seal the barrel and wait at least 24 hours before consuming.

The water should have a slight chlorine odor. If not, repeat the process. See our post Tips for Storing Water in a 55-Gallon Plastic Barrel for detailed instructions.


Iodine is available in tablet, liquid, and crystalline forms. It will effectively deactivate most pathogens in water, with the exception of some protozoa such as cryptosporidium.

Pregnant women or individuals with thyroid problems should not use iodine. Long-term use of iodine for water purification is not recommended.

Water pH and temperature will impact the required amount of iodine. The shelf-life varies with each form of iodine. Tablets may have a shelf life of only two years while crystalline iodine is good indefinitely.

Iodine Tablets

Potable Agua (tetraglycine hydroperiodide) is a tablet form of iodine used by the military for field water treatment in canteens and by outdoor enthusiasts. Thirty minutes of contact time is required for the deactivation of pathogens.

The manufacturer recommends a four-year shelf life for an unopened bottle and only one year once the package is opened. Exposure to heat, humidity, moisture, and air will reduce effectiveness.

Tincture of Iodine

The tincture of iodine is the common household form of iodine found in many first aid kits. The U.S. Army Center for Health Promotion and Preventative Medicine recommends adding 5 drops of 2 percent United States Pharmacopeia (U.S.P.) Tincture of Iodine to each quart of clear water.

Allow at least 30 minutes of contact time before drinking. Cloudy water may require twice that amount of iodine.

Crystalline Iodine

Polar Pure is a crystalline form of iodine. It has an indefinite shelf life and one bottle will disinfect 2000 liters of water. Water is added to the crystals in the bottle, creating a stock solution.

An indicator dot on the side of the bottle indicates the amount of iodine required for water disinfection depending on the temperature. The iodine saturation rate of the stock solution is higher at warmer temperatures.

Add the recommended amount of iodine solution to the clarified water and allow it to stand for 20 minutes before consuming. The Polar Pure bottle should be refilled with water to ensure the stock solution is ready for use when needed.

Note: This product may be difficult to obtain and has recently undergone some changes. It may be wise to do a little bit of investigation on your own before purchasing.

Solar Water Disinfection (SODIS)

SODIS is an incredible survival trick that you should remember. All harmful dangerous pathogens in water can be deactivated with a plastic bottle and sunshine. Honest! I did not believe this at first, so I thoroughly researched it and am now convinced that it will effectively disinfect water.

UV (Ultraviolet) disinfection will deactivate all bacteria, and viruses and even kill the protozoa which are resistant to chlorine and iodine treatment. It may sound too good to be true, but the fact is millions of people use this method every day in developing countries to provide safe drinking water for their families.

SODIS works as the UV-A light irradiate the microorganisms while the infrared light heats the water. Several factors contribute to the death of microorganisms and pathogens including; light, temperature, nutrition, humidity, and time. SODIS will not remove chemicals, tastes, or smells. It will not treat large volumes of water. The transparent container should not be larger than 4 inches in diameter.

Learn more about SODIS at UV Rays Save the Day—Disinfecting Water with the Sun where we demonstrate step-by-step instructions on solar water disinfection.

Solar water disinfection is amazingly simple and effective. Just follow these simple guidelines to enjoy safe water:

  • Start with a clean, transparent container no larger than four inches in diameter. Clear food-grade plastic water bottles, plastic soda bottles (1-2 liter), or glass jars with tight-fitting lids work well.
  • Use the cleanest water available. Clarify to remove larger particles by filtering the water through a piece of cloth.
  • Fill bottle part way with water and shake vigorously. This will saturate the water with oxygen and increase performance in sunlight. Then finish filling the bottle.
  • Place the bottle horizontally, on its side, to allow maximum exposure to the sunlight. Dark surfaces increase the temperature of the water and disinfection will occur faster.
  • A clear sunny day, or even a partly cloudy day, will disinfect water in 5 to 6 hours. Expose the bottle for 2 consecutive days if the sky is completely covered with clouds to ensure disinfection.
  • Water should be cooled completely before drinking.

Seriously, it sounds too good to be true … but it is true. A transparent bottle, time, and sunshine may just protect you from acquiring the waterborne illness. All you have to do is understand the basics and apply them correctly. Visit to learn more.

Step #3 – Filtration

Water filters screen out particles and are effective against pathogens down to a specified size. Many filters are unable to catch tiny viruses. Water purifiers filter out chemicals and some biobugs as well as use another method to kill the viruses which may get through the filter.

When using a water filter, it is a good idea to disinfect the water before running it through the filter. The filter may remove the chemical taste and odor, making it more pleasant to drink. The cleaner the water you put into the filter, the longer your filter will last.

All filters are not created equal. Only a few are rated to filter out viruses and do not require disinfecting prior to filtration. Understand the limitations of your filter and use it correctly to produce safe clean drinking water.

Gravity Filters

Gravity filters use gravity to pull the water through the filter. Water is poured into the top of the container, filtered, and accessed through a spigot at the bottom. These filters range from high-end stainless steel filters to do-it-yourself 5-gallon bucket filters to collapsible bag filters. Whatever the container, it is the actual filter inside that determines the level of filtration.

Some gravity filters are not easily transported, but are great for use on a counter-top in emergencies or for everyday use. They produce large amounts of clean drinking water. Do not allow wet filters to freeze. They may crack and become ineffective.

Examples of gravity filters are AquaRain, Berkey, Katadyn Gravity Camp, MSR Autoflow Gravity Filter, Sawyer PointONE or Point ZeroTWO Purifier with Bucket Adapter Kit, and Hydroblu Gravity Water Filter Bag.

One of the best water purifiers on the market is Berkey. The Berkey filters can remove all biological pathogens and most of the chemical contaminants. Learn more at USA Berkey Filters. Use the promo code Provident10 to get 10% off your entire order. 

Pump Filters

Pump filters typically use a hand pump to force the water through the filter in order to clean the water. These come in different sizes from portable individual pumps to larger pumps designed to service many people.

Examples of pump filter include Katadyn Expedition, Katadyn Pocket, MSR Miniworks Ex Microfilter, Seychelle Pure Water Pump, Survivor Filter Pro, and Hydroblu Pressurized Jerry Can. The Hydroblu Versa Flow Inline Water Filter is pictured. Notice how the dirty water passes through the filter and comes out clear in the water bottle below.

Suction Filters

Water is sucked through the filter by the individual at the point of consumption. One area of concern is the close proximity of your face to the contaminated water and the possibility of accidental contamination.

Suction filters are highly portable. Hydration pack filters can be quite convenient when traveling by foot.

Examples of suction filters include; LifeStraw Personal Water Filter, Seychelle Pure Water Straw, Sawyer Products Mini Water Filtration System for Hydration Packs and Hydroblu Sidekick 3-Stage Straw Water Filter.

Water Filter Bottles

Water filter bottles are a good option for personal water filtration needs. They are perfect tools to improve the taste and safety of the water in everyday life.

Bottles are lightweight and ideal for emergency kits or to throw into a suitcase or backpack when traveling. Each bottle is unique in the amount of water it will filter, the price, and the overall effectiveness of the filter.

Examples of water filter bottles include; Life Straw Water Filter Bottle, Sawyer Personal Water Filter Bottle, Seychelle Water Filtration Bottle, Purewell Water Filter Bottle, and Sport Berkey Water Purification Bottle.

Bringing it Home

Safe drinking water is created by deactivating all biological pathogens (protozoa, bacteria, and viruses) as well as physically removing chemical contaminants (salt, pesticides, heavy metals, pollutants, etc.).

We have reviewed a variety of options for water disinfection and purification. Remember, you need to be able to kill the tiny viruses which some filters cannot remove as well as filter out the larger protozoa that are resistant to chemical disinfection.

The best way to ensure your water is safe to drink is with a combination of disinfection and filtration. Water stored in your own home is the safest water source you can have in an emergency. Make water storage, as well as water disinfection and filtration, a part of your family emergency plan. You can do this!

Thanks for being part of the solution!

Jonathan and Kylene Jones


Kylene Jones is a blogger, content creator, published author, motivational speaker, homesteader, prepper, mother, and grandmother. She practices self-reliance, provident living, and emergency preparedness in her everyday life. She loves working with her husband, Jonathan, and is committed to helping our community be prepared to thrive during the challenges that lie in our future.

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