In an emergency, water contaminated with germs can often be made safe to drink by boiling, adding disinfectants, or filtering.
IMPORTANT: Water contaminated with fuel or toxic chemicals will not be made safe by boiling or disinfection. Use bottled water or a different source of water if you know or suspect that your water might be contaminated with fuel or toxic chemicals.
In emergency situations, use bottled water if possible; bottled water is the safest choice for drinking and all other uses. If bottled water is not available, the following methods can help make your water safe to drink.
*Note: These methods are listed in order of what is most effective at making your water safe.
1. Boiling
If you don’t have safe bottled water, you should boil your water to make it safe to drink. Boiling is the surest method to kill disease-causing organisms, including viruses, bacteria, and parasites.
You can improve the flat taste of boiled water by pouring it from one container to another and then allowing it to stand for a few hours, OR by adding a pinch of salt for each quart or liter of boiled water.
If the water is cloudy:
Filter it through a clean cloth, paper towel, or coffee filter OR allow it to settle.
Draw off the clear water.
Bring the clear water to a rolling boil for 1 minute (at elevations above 6,500 feet, boil for three minutes).
Let the boiled water cool.
Store the boiled water in clean sanitized containers with tight covers.
If the water is clear:
Bring the clear water to a rolling boil for 1 minute (at elevations above 6,500 feet, boil for three minutes).
Let the boiled water cool.
Store the boiled water in clean sanitized containers with tight covers.
2. Disinfectants
If you don’t have safe bottled water and if boiling is not possible, you often can make small quantities of filtered and settled water safer to drink by using a chemical disinfectant such as unscented household chlorine bleach. Disinfectants can kill most harmful or disease-causing viruses and bacteria, but are not as effective in controlling more resistant organisms, such as the parasites Cryptosporidium and Giardia. Chlorine dioxide tablets can be effective against Cryptosporidium if the manufacturer’s instructions are followed correctly. If the water is contaminated with a chemical, adding a disinfectant will not make it drinkable. To disinfect water with tablets that contain chlorine or iodine:
Follow the manufacturer’s instructions on the label or in the package.
Chlorine dioxide tablets can be effective against Cryptosporidium if the manufacturer’s instructions are followed correctly.
Iodine and iodine-containing tablets (tetraglycine hydroperiodide) or chlorine tablets are not effective against Cryptosporidium.
To disinfect water with unscented household liquid chlorine bleach:
If the water is cloudy:
Filter it through a clean cloth, paper towel, or coffee filter OR allow it to settle.
Draw off the clear water.
Follow the instructions for disinfecting drinking water that are written on the label of the bleach.
If the necessary instructions are not given, check the “Active Ingredient” part of the label to find the sodium hypochlorite percentage, and use the information in the following table as a guide. Typically, unscented household liquid chlorine bleach in the United States will be between 5-8.25% sodium hypochlorite, though concentrations can be different in other countries. Using the table below, add the appropriate amount of bleach using a medicine dropper, teaspoon, or metric measure (milliliters).
Stir the mixture well.
Let it stand for at least 30 minutes before you use it.
Store the disinfected water in clean, sanitized containers with tight covers.
If the water is clear:
Follow the instructions for disinfecting drinking water that are written on the label of the bleach.
If the necessary instructions are not given, check the “Active Ingredient” part of the label to find the sodium hypochlorite percentage, and use the information in the following table as a guide. Typically, unscented household liquid chlorine bleach in the United States will be between 5-8.25% sodium hypochlorite, though concentrations can be different in other countries. Using the table below, add the appropriate amount of bleach using a medicine dropper, teaspoon, or metric measure (milliliters).
Stir the mixture well.
Let it stand for at least 30 minutes before you use it.
Store the disinfected water in clean, sanitized containers with tight covers.
| Making water safe to use with bleach having a 1% concentration of sodium hypochlorite * If the water is cloudy, murky, colored, or very cold, add double the amount of bleach listed below |
||
|---|---|---|
| 1 quart/liter water |
1 gallon water |
5 gallons water |
| If you have a dropper: Add 10 drops of bleach |
If you have a dropper: Add 40 drops of bleach |
If you have a dropper: Add 200 drops of bleach |
| If you have something that measures milliliters (ml): Add ½ ml of bleach |
If you have something that measures milliliters (ml): Add 2½ ml of bleach |
If you have something that measures milliliters (ml): Add 12½ ml of bleach |
| If you have a measuring spoon: Add ⅛ teaspoon of bleach |
If you have a measuring spoon: Add ½ teaspoon of bleach |
If you have a measuring spoon: Add 2½ teaspoons of bleach |
| Making water safe to use with bleach having a 1% concentration of sodium hypochlorite * If the water is cloudy, murky, colored, or very cold, add double the amount of bleach listed below |
||
|---|---|---|
| 1 quart/liter water |
1 gallon water |
5 gallons water |
| If you have a dropper: Add 10 drops of bleach |
If you have a dropper: Add 40 drops of bleach |
If you have a dropper: Add 200 drops of bleach |
| If you have something that measures milliliters (ml): Add ½ ml of bleach |
If you have something that measures milliliters (ml): Add 2½ ml of bleach |
If you have something that measures milliliters (ml): Add 12½ ml of bleach |
| If you have a measuring spoon: Add ⅛ teaspoon of bleach |
If you have a measuring spoon: Add ½ teaspoon of bleach |
If you have a measuring spoon: Add 2½ teaspoons of bleach |
3. Filters
Many portable water filters can remove disease-causing parasites such as Cryptosporidium and Giardia from drinking water. If you are choosing a portable water filter, try to pick one that has a filter pore size small enough to remove parasites. Most portable water filters do not remove bacteria or viruses.
Carefully read and follow the manufacturer’s instructions for the water filter you intend to use. After filtering, add a disinfectant such as iodine, chlorine, or chlorine dioxide to the filtered water to kill any viruses and remaining bacteria.
Filtering Tap Water
Many but not all available home water filters remove Cryptosporidium. Some filter designs are more suitable for removal of Cryptosporidium than others. Filters that have the words “reverse osmosis” on the label protect against Cryptosporidium. Some other types of filters that function by micro-straining also work. Look for a filter that has a pore size of 1 micron or less. This will remove microbes 1 micron or greater in diameter (Cryptosporidium, Giardia). There are two types of these filters — “absolute 1 micron” filters and “nominal 1 micron” filters but not all filters that are supposed to remove objects 1 micron or larger from water are the same. The absolute 1 micron filter will more consistently remove Cryptosporidium than a nominal filter. Some nominal 1 micron filters will allow 20% to 30% of 1 micron particles (like Cryptosporidium) to pass through.
Filter manufacturers may pay to have their filters tested to see if they remove Cryptosporidium or Giardia. Filters that have been tested and certified should have wording on their labels indicating they have been listed and labeled to NSF/ANSI Standard 53 or Standard 58 for cyst removal or cyst reduction by an ANSI-accredited certification organization. To find out if a particular filter is certified to remove Cryptosporidium, you can look for “NSF 53” or “NSF 58” plus the words “cyst reduction” or “cyst removal” on the product label information. If you chose to use a non-certified product, select those technologies more likely to reduce Cryptosporidium, including filters with reverse osmosis and those that have an absolute pore size of 1 micron or smaller.
Because filter testing is expensive and voluntary, some filters that may work against Cryptosporidium may not have been tested. If you chose to use a product not labeled “NSF 53” or “NSF 58”, select those technologies more likely to reduce Cryptosporidium, including filters with reverse osmosis and those that have an absolute pore size of 1 micron or smaller.
Filters designed to remove Crypto (any of the four messages below on a package label indicate that the filter should be able to remove Crypto)
Reverse osmosis (with or without NSF 53 or NSF 58 labeling)
Absolute pore size of 1 micron or smaller (with or without NSF 53 or NSF 58 labeling)
Tested and certified to NSF/ANSI Standard 53 or NSF/ANSI Standard 58 for cyst removal
Tested and certified to NSF/ANSI Standard 53 or NSF/ANSI Standard 58 for cyst reduction
Filters labeled only with these words may NOT be designed to remove Crypto
Nominal pore size of 1 micron or smaller
One micron filter
Effective against Giardia
Effective against parasites
Carbon filter
Water purifier
EPA approved (Caution: EPA does not approve or test filters)
EPA registered (Caution: EPA does not register filters based on their ability to remove Cryptosporidium)
Activated carbon
Removes chlorine
Ultraviolet light
Pentiodide resins
Water softener
Chlorinated
Note: Filters collect germs from water, so someone who is not immunocompromised should change the filter cartridges. Anyone changing the cartridges should wear gloves and wash hands afterwards. Filters may not remove Cryptosporidium as well as boiling does because even good brands of filters may sometimes have manufacturing flaws that allow small numbers of Cryptosporidium to get in past the filter. Selection of certified filters provides additional assurance against such flaws. Also, poor filter maintenance or failure to replace the filter cartridges as recommended by the manufacturer can cause a filter to fail.
4. Distillation
You may also be able to make water safe by distilling it or by boiling water and collecting the steam in a clean container so it turns back into water.
Learn more about distilling water:
FEMA/American Red Cross. Food and Water in an Emergency.pdf [PDF – 16 pages]
Other Methods
Water Disinfection
Travelers who are heading to remote places to camp or hike or staying in locations with unknown water quality may need to disinfect their drinking water. Bottled water is a convenient solution, but the plastic bottles create an ecological problem. Some methods to ensure safe drinking water are described below.
Heat
Most germs die quickly at high temperatures. Water that has been boiled for 1 minute is safe to drink after it has cooled. If no other means of water treatment is available, an alternative to boiling is to use tap water that is too hot to touch, which is probably at a temperature between 131°F (55°C) and 140°F (60°C). This temperature may be adequate to kill pathogens if the water has been kept hot for some time. Travelers with access to electricity can bring a small electric heating coil or a lightweight beverage warmer to boil water.
Filtering
A variety of filters are available from camping stores. Most have filter sizes between 0.1 and 0.4 microns, which will remove bacteria from water but may not remove viruses. Reverse osmosis filters remove bacteria and viruses and can also remove salt from water, which is important for ocean voyagers.
Chemicals
Tablets or packets of powder can be bought at camping stores to disinfect water. These usually combine chemical disinfectants (such as chlorine or iodine) with a substance that makes the water clear and improves its taste. Follow the instructions on the package closely—you may need to wait several hours until all the germs are killed. Household bleach can also be used to disinfect water.
Ultraviolet (UV) Light
Portable units that deliver a measured dose of UV light are effective to disinfect small quantities of clear water. However, this technique is less effective in cloudy water because small particles may shield germs from the light.
Solar Radiation
In emergencies, sunlight in the UVA range can substantially improve the quality of water. In cloudy weather, water must be placed in the sun for 2 consecutive days.
Solar disinfection is not effective on cloudy, opaque water. If the headlines in a newspaper cannot be read through the bottle of water, the water must be clarified before solar irradiation is used.
More Information
EPA. Emergency Disinfection of Drinking Water. Guidelines in emergency disinfection of drinking water with PDF documents in English, Spanish, French, Arabic, and Vietnamese.
EPA. Safe Drinking Water Hotline (800-426-4791).
CDC. A Guide to Commercially-Bottled Water and Other Beverages.
Drinking Water Treatment and Sanitation for Backcountry & Travel Use
Introduction
This information should only serve as a guide for individuals intending to use untreated or poorly treated water as a drinking source. This document may also aid travelers and backcountry water users in researching drinking water treatment methods. Except for boiling, few of the water treatment methods are 100% effective in removing all pathogens.
Protozoa - Cryptosporidium
Potential health effects from ingestion of water contaminated with Cryptosporidium are:
Gastrointestinal illness (for example, diarrhea, vomiting, cramps).
Sources of Cryptosporidium in drinking water are:
Human and animal fecal waste.
Methods that may remove some or all of Cryptosporidium from drinking water are:
Boiling (Rolling boil for 1 minute) has a very high effectiveness in killing Cryptosporidium;
Filtration has a high effectiveness in removing Cryptosporidium when using an absolute less than or equal to 1 micron filter (NSF Standard 53 or 58 rated “cyst reduction / removal” filter);
Disinfection with iodine or chlorine is not effective in killing Cryptosporidium;
Disinfection with chlorine dioxide has a low to moderate effectiveness in killing Cryptosporidium;
Combination filtration and disinfection has a very high effectiveness in removing and killing Cryptosporidium when used with chlorine dioxide and an absolute less than or equal to 1 micron filter (NSF Standard 53 or 58 rated “cyst reduction / removal” filter).
Protozoa - Giardia intestinalis (also known as Giardia lamblia)
Potential health effects from ingestion of water contaminated with Giardia are:
Gastrointestinal illness (for example, diarrhea, vomiting, cramps).
Sources of Giardia in drinking water are:
Human and animal fecal waste.
Methods that may remove some or all of Giardia from drinking water are:
Boiling (Rolling boil for 1 minute) has a very high effectiveness in killing Giardia;
Filtration has a high effectiveness in removing Giardia when using an absolute less than or equal to 1 micron filter (NSF Standard 53 or 58 rated “cyst reduction / removal” filter);
Disinfection with iodine or chlorine has a low to moderate effectiveness in killing Giardia;
Disinfection with chlorine dioxide has a high effectiveness in killing Giardia;
Combination filtration and disinfection has a very high effectiveness in removing and killing Giardia when used with chlorine dioxide and an absolute less than or equal to 1 micron filter (NSF Standard 53 or 58 rated “cyst reduction / removal” filter).
Bacteria - (for example, Campylobacter, Salmonella, Shigella, E. coli)
Potential health effects from ingestion of water contaminated with bacteria are:
Gastrointestinal illness (for example, diarrhea, vomiting, cramps).
Sources of bacteria in drinking water are:
Human and animal fecal waste.
Methods that may remove some or all of bacteria from drinking water are:
Boiling (Rolling boil for 1 minute) has a very high effectiveness in killing bacteria;
Filtration has a moderate effectiveness in removing bacteria when using an absolute less than or equal to 0.3 micron filter;
Disinfection with iodine or chlorine has a high effectiveness in killing bacteria;
Disinfection with chlorine dioxide has a high effectiveness in killing bacteria;
Combination filtration and disinfection has a very high effectiveness in removing and killing bacteria when used with iodine, chlorine, or chlorine dioxide and an absolute less than or equal to 0.3 micron filter (NSF Standard 53 or 58 rated “cyst reduction / removal” filter).
Viruses - (for example, enterovirus, hepatitis A, norovirus, rotavirus)
Potential health effects from ingestion of water contaminated with viruses are:
Gastrointestinal illness (for example, diarrhea, vomiting, cramps), hepatitis, meningitis.
Sources of viruses in drinking water are:
Human and animal fecal waste.
Methods that may remove some or all of viruses from drinking water are:
Boiling (Rolling boil for 1 minute minimum) has a very high effectiveness in killing viruses;
Filtration is not effective in removing viruses;
Disinfection with iodine or chlorine has a high effectiveness in killing viruses;
Disinfection with chlorine dioxide has a high effectiveness in killing viruses;
Disinfection has a high effectiveness in killing viruses when used with iodine, chlorine, or chlorine dioxide.
Things to Remember
Please remember that:
Boiling can be used as a pathogen reduction method that should kill all pathogens. Water should be brought to a rolling boil for 1 minute. At altitudes greater than 6,562 feet (greater than 2000 meters), you should boil water for 3 minutes.
Filtration can be used as a pathogen reduction method against most microorganisms, depending on the pore size of the filter, amount of the contaminant, particle size of the contaminant, and charge of the contaminant particle. Manufacturer’s instructions must be followed. Only filters that contain a chemical disinfectant matrix will be effective against some viruses.
Disinfection can be used as a pathogen reduction method against microorganisms. However, contact time, disinfectant concentration, water temperature, water turbidity (cloudiness), water pH, and many other factors can impact the effectiveness of chemical disinfection. The length of time and concentration of disinfectant varies by manufacturer and effectiveness of pathogen reduction depends on the product. Depending on these factors, 100% effectiveness may not be achieved. Manufacturer’s instructions must be followed.
If boiling water is not possible, a combination of filtration and chemical disinfection is the most effective pathogen reduction method in drinking water for backcountry or travel use. Manufacturer’s instructions must be followed.
Other treatment methods can be effective against some of the above pathogens:
Ultraviolet Light (UV Light) can be used as a pathogen reduction method against some microorganisms. The technology requires effective prefiltering due to its dependence on low water turbidity (cloudiness), the correct power delivery, and correct contact times to achieve maximum pathogen reduction. UV might be an effective method in pathogen reduction in backcountry water; there is a lack of independent testing data available on specific systems. Manufacturer’s instructions must be followed.
MIOX® systems use a salt solution to create mixed oxidants, primarily chlorine. Chlorine has a low to moderate effectiveness in killing Giardia, and a high effectiveness in killing bacteria and viruses. Manufacturer’s instructions must be followed.
Important: Water that has been disinfected with iodine is NOT recommended for pregnant women, people with thyroid problems, those with known hypersensitivity to iodine, or continuous use for more than a few weeks at a time.
Sanitation
In addition to using the appropriate drinking water treatment methods listed above, you can also protect yourself and others from waterborne illness in the backcountry or while traveling by paying attention to good sanitation practices:
Burying human waste 8 inches deep and at least 200 feet away from natural waters.
Practicing good personal hygiene. Wash hands before handling food, eating, and after using the toilet.