How to Sterilize Water When a Disaster Happens

sterilize water
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How to sterilize water when a disaster happens

In late 1981, sailing enthusiast and marine racing participant Steven Callahan ran afoul of a storm on a sea race route from Cornwall, England, to the island of Antigua in the Caribbean. The storm sank several racing boats off the coast of northern Spain — and Callahan, in his 21.3-foot boat the Napoleon Solo, had to drop out of the race. By early 1982, Callahan set out to sea again, this time from the Canaries, and intended to go to Antigua by himself.

However, damage to the Napoleon Solo‘s hull (perhaps caused by a whale) left Callahan no option but to abandon ship. He got into a small lifeboat and salvaged flares, navigation charts, a spear gun, some food, and a sea survival manual from the Solo. Perhaps most importantly, Callahan took a marine solar still — a device that is used to retrieve and purify seawater in a condensation process, using the heat from sunlight. With this device, Callahan was able to produce a little under a pint of drinking water a day.

sterilize water

Over seventy-five days later, Callahan saw lights from the island of Marie-Galante, part of the Guadaloupe archipelago. Some local fishermen had followed a flock of birds that were hovering over Callahan’s craft. They spotted him and brought him to safety. Callahan had been rescued.

A ‘regular’ disaster

Callahan’s story is not a typical scenario of disaster preparedness. Most disaster scenarios are land-based and anticipate fires, floods, or devastating storms. However, the methods used to sterilize water in these situations are often very similar. If you want to purify or sterilize water with a solar still, for example, you don’t necessarily have to be at sea.

Perhaps you already are familiar with collecting water safely and quickly, with some basic ideas of how to sterilize water for emergency situations. But for prolonged periods of sheltering in — or impromptu journeys to avoid danger, you might need more detailed information. You will have to keep in mind the following contingencies:

  • Being able to sterilize water for sheltering in place, known as a ‘Bugging In’ scenario,
  • Being able to sterilize water during travel and evacuations, also known as a ‘Bugging Out’ scenario, and
  • Being able to store water in both situations.

How to sterilize water in a ‘bugging in’ scenario

In an emergency scenario, ‘bugging in’ usually means staying or sheltering in your home (or current place of residence) until the danger from a disaster has passed. Power outages, blizzards, earthquakes, droughts, and pandemic quarantines are all examples of disaster scenarios in which you may have to ‘bug in’.

A bugging in scenario does always not have to be extreme. It could be as simple as having the tap water running into contamination or running out completely. In this case, having an on-hand supply of bottled water should be your first choice — but sterilization techniques can still come in handy. Here are some of them:

  • Filtering water,
  • Boiling water,
  • Bleaching water, and
  • Using disinfecting products.

Filtering water

The United States Environmental Protection Agency (EPA) recommends having an emergency supply of water for ready drinking. Unopened bottled water should be your first option. 

For any other source, the EPA says to look at the water you want to use. If the water is cloudy or otherwise dirty, let it settle first. Then take a paper towel, coffee filter, or clean piece of cloth and filter the clearer water on top into a clean container. Finally, store the filtered water by covering the container.

Boiling water

Boiling water is a way to get rid of organic contaminants – protozoa, viruses, and bacteria. A combination of filtering and boiling is recommended by the EPA, so make sure you filter your water before you boil it. 

Once the filtered water is in a clean container, find a similarly clean vessel to boil your water. Put the water in, let it reach a rolling boil and boil for at least one minute. For higher altitudes (at or over 5000 feet, or 1524 meters) let the water boil for at least three minutes. To help with taste, add a pinch of salt for each quart/liter of water.

Let the water cool at a natural rate. Store it in a clean container with a cover.

Bleaching water

The EPA recommends using household bleach to sterilize water if boiling is not an option. But make sure that the bleach you use is a regular, unscented, chlorine bleach that is suitable for sterilization according to its label. The label will also say what percentage of the active ingredient sodium hypochlorite is in the bleach. 

Usually it is 6% or 8.25% sodium hypochlorite (most unscented bleaches in the United States are in these low percentage ranges, but elsewhere the percentages can be different) and you will have to use bleach stored at room temperatures for less than one year. 

Using a clean medicine dropper, drop 8 drops of 6% sodium hypochlorite bleach per gallon of water. If you use 8.25% sodium hypochlorite bleach, use 6 drops per gallon of water. 

Stir and let stand for 30 minutes. The water should smell slightly of chlorine. If it doesn’t, add another dosage and let stand for another 15 minutes. If chlorine taste is too strong, move the water to another clean container. Then let stand for a few hours.  
It is highly recommended to carefully review the EPA site for proportions and details about bleaching water.

Disinfecting products

Filtering and boiling should be your first options to sterilize water, but a household might have other chemical products designed for the same purpose. These can include:

  • Granular calcium hypochlorite (HTH), 
  • Household iodine, and 
  • Store-bought disinfecting tablets that may contain chlorine dioxide, iodine, chlorine, or other chemicals.

However, these chemicals can be dangerous to handle and use. HTH, for example, is a powerful oxidant and must be used in a ventilated area. Iodine is not recommended for pregnant women or those with thyroid conditions. Always consult the EPA site or call the Safe Drinking Water Hotline (800) 426 -4791 for details of their use.

How to sterilize water in a ‘Bugging Out’ scenario

Another reaction to an emergency scenario is ‘bugging out’. Bugging out refers to leaving your home or shelter to put some distance between you and the source of danger. Evacuations from hurricanes, coastal floods, volcanoes, or tornadoes are all examples of disaster scenarios in which residents have had to ‘bug out’.

If unopened bottled water is unavailable in a bug out scenario, you will need to sterilize water using lightweight, portable methods. These can include:

  • Boiling water,
  • Survival Straws,
  • UV Light Devices, and
  • Solar Stills.

Boiling water

If boiling water seems like something important enough to mention twice on the same list, that’s because it is! Filtering and boiling water are almost unmatched in effectiveness in sterilizing water from various harmful parasitic microorganisms — and both the EPA and the United States’ Centers for Disease Control and Prevention (CDC) recommend it. 

In a bug out scenario, however, you will want to make sure you can carry clean containers that can stay clean. You will want containers that are portable, but can carry enough water for you and the members of your party. 

Finally, you will want to have containers that can be used to boil water. You can’t use a plastic or synthetic container to boil water. But you can use a clean can, or a metal pot or pan. As always, filter first, boil accordingly, let the water cool naturally, pour into a clean container, and cover.

Survival Straws

There is a difference between water filtration and water purification. The boiling and chemical treatment methods described above are water purification methods, designed to get rid of organic contaminants, and in some cases, other chemicals. Purification through evaporation, or distillation (like Callahan’s solar still), is another water purification method.

These purification methods often are combined with filtration methods (like pouring water through a coffee filter or clean cloth) to eliminate particles or sediments in the water.

But another filtration method is to use a survival straw. These are brand-name products that are sold online or in stores. Designed to match EPA standards, these straws claim to filter bacteria like cholera, E. coli, and salmonella, as well as microscopic plastic contaminants. They do this through small micro-filters made of materials such as carbon. 

It is best to research these products and know their limitations. Some can filter more water at a time, some less. Some have a carbon or metal aftertaste. But for the most part, survival straws are lightweight and portable enough for quick use in a bug out scenario.

UV light devices

Another portable water purification method are Ultraviolet (UV) light devices. These are small, often hand-held devices that use UV light to kill protozoa, viruses, bacteria, and molds. Place the wand or pen-like bulb into your water and turn it on. The device will kill most organic contaminants.

The advantage of using these devices is the lack of chemicals needed to achieve sterilization. They are also small and easy to carry, and less time is needed to purify water than boiling methods. Finally, they can disable Cryptosporidium and Giardia, two parasites that chemical methods (like bleaching) often do not kill. 

However, there are several disadvantages to UV light devices. They do not filter out sediments or chemicals (though some devices come with separate sediment treatment tools). They are often battery-operated, or need some other energy source to operate. They can be fragile. Finally, though UV devices can kill most microorganisms, they do not remove them from the water like filtration methods.

Like survival straws, UV devices have their own limitations and are not a cure-all. But they are effective for some water purification. It is best to do sufficient research and have this tool as one part of your water sterilization plan.

Solar stills

The process of distillation separates materials in a liquid mixture through a process of boiling and condensation. If not boiled entirely, distillation can occur through slower processes of evaporation (and then condensation). This is how Steven Callahan was able to desalinize his drinking water – distillation through a solar still. 

A solar still is a device that in essence is a smaller container inside a larger, covered container. The larger container can contain saltwater or otherwise impure water. When the solar still is exposed to light or heat, the water evaporates and collects on the underside of the top of the larger container. The evaporated water then drips down into the smaller container. 

The advantage of a solar still is that distilled water can remove salts and other minerals. This is very important if you are only around a lot of sea water. However, a solar still takes time to use, and unless it is small, it is not very portable. Also, the distilled water may still need to purified through filtration and boiling. 

Depending if you are ‘on the go’, near an ocean, or have a place to store it, a solar still can be of use. Distillation is nevertheless a good way to separate larger particulate matter from your water. 

Storing water

If you are ‘bugging in’, use containers that are better suited for long hauls, or at least until the crisis is over. Be careful not to let the water stagnate and use clean, covered containers.

If you are ‘bugging out’, be sure to use portable containers. Bottles or light containers with lids will not weigh you down. A pot or pan, for boiling, may benefit from having a lid, too.  

In either case, use clean, covered containers and remember to use your water in a timely fashion. This way, you will make ready use of your sterilized water in the event of a disaster.



Adrift: Seventy-six Days Lost at Sea by Steven Callahan:


Popular Mechanics, January 1954:











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