Even if you are the strongest person on the planet or have the toughest fallout bunker in North America, you won’t last too long in a disaster without a reliable source of life’s most basic element—water. After the last bite of a double cheeseburger, your body can survive without food for roughly three weeks, but that last sip of soda will keep you going for less than a week. In extreme conditions, it only takes a few days before your body reaches the point of dehydration that can be fatal. Quite frankly, drinking water might be the most important thing to consider when planning for your survival after a major disaster.

Stock Up

If you haven’t already, go to the local market and buy a stockpile of clean drinking water; this is the easiest source of water for disasters. The rule of thumb for emergency water storage is 1 gallon per person per day; this ensures a half a gallon for drinking and the other half for hygiene purposes. It is recommended you store enough emergency water to last for three days, but it is up to you to determine the amount you want to store, and this is mainly constrained by the amount of storage space you have. One popular option for large storage amounts is the 55-gallon water barrels that are BPA-free and made with food-grade plastic. Technically, if your water is sterile and stored properly, it should last forever, though it’s wise to change the water out every year or two just to be on the safe side.

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Embrace Your Inner Germophobe

There is still a likelihood that your stockpiled water source has been contaminated, and in worst-case scenarios, your water can run out. Don’t despair, as science and a level head can get you through these times of crisis. The ultimate goal of water safety is to purify and sterilize water to a point where there are no harmful chemicals or microorganisms in the water. Removing chemicals from water is tricky, and there is no reliable method of doing this during a crisis. Purifying using a distillation method requires that you know the differences between the boiling points of water and the chemicals of interest, but most likely you will not know the specific chemicals that have tainted the water. Also, distillation requires technical knowledge and specific equipment, which few people possess—unless, of course, you are one of those who make their own moonshine late at night. An alternative method, carbon filtration, will remove some but not all types of chemicals.

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Reach Your Boiling Point

Although purification is not foolproof, sterilization will get rid of nasty microscopic bugs. The most effective way to make sure your water is safe to drink is to boil it. This method is the preferred way of sterilizing your water anywhere and anytime you have a heat source. Water should be boiled at least a minute, and over three minutes if you are 5,000 feet or more above sea level.

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If boiling is not an option, the simplest way to sterilize water is to chlorinate it by adding perfume-free household bleach. Before using bleach on your water, make sure the water is as free of sediment as possible. This can be achieved by letting cloudy water sit, allowing the sediment to settle at the bottom, or you can filter the water through clean fabric to get rid of larger particles. For every gallon of water, add one eighth of a teaspoon of bleach to your water and let it stand for 30 minutes. By this point it should have a slight chlorine smell. So, along with your guns and knives, make sure you have a stock of bleach readily available in your prepper arsenal. One important note: Chlorine does expire in storage and usually degrades about 20 percent per year.

Truly hardcore preppers will get around this problem by storing granular calcium hypochlorite, which is available in pool supply stores and online. Used correctly, it works like bleach, but the solid granules can be stored for a long time. Granular calcium hypochlorite is very hazardous and requires proper storage in a cool, dry location, and the chemical should be placed in a sealed amber glass. To disinfect water, you first add a tablespoon of granular calcium hypochlorite (70-percent chemical content) to 2 gallons of water to make a stock solution. You then mix one part of this stock solution with 100 parts water and let it sit for 30 minutes before drinking (never attempt without first consulting an expert).

Not-So-Mellow Yellow

Often during a real crisis, being mobile is important, and this will change the way you acquire drinking water. Since water is heavy, carrying water is not practical. Therefore, finding water as you travel will be a necessity. There are a few options to choose from, with both benefits and shortcomings to each. Before we can use any of these methods, a source of water must be found. Snow is obviously a great water source, but look for snow that is white and not dirty or yellow—no explanation is needed here. Most clean white snow is safe, but make sure to melt the snow first, because eating snow can lower your body temperature and lead to hypothermia. Another gift from Mother Nature can come in the form of rainwater. Most rainwater that is collected as it falls is safe, but avoid drinking untreated runoff rainwater. If the nearby atmosphere is polluted with toxic substances, then the rain that falls within that area will most likely carry that pollutant, so stay clear of drinking this rainwater.

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When relying on water from natural sources, first look for clear running water that does not have much sediment or visible particulates in it. Springs and streams are excellent sources of water, but there is no guarantee that they’ll be safe to drink. One item of note is that flowing water at higher elevations is more likely safer to drink than water at lower elevations, so take this into consideration when choosing whether to treat the water before drinking. Water from larger bodies of water, such as lakes and ponds, is not ideal, because stagnant water allows for better growth of microorganisms, requiring treatment of the water.

Keeping Tabs

Other than boiling the water, one of the easiest and most effective options for water treatment is using iodine tablets. This method of chemical treatment has been used for decades to kill microorganisms in water, but it can leave a strong and displeasant taste.

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There are also readily available filter-style apparatuses that are very effective at getting rid of bacteria and protozoa. Portable filter systems are commonly designed with pumps that help move water through a porous material that allows only particles less than 0.2 microns in size to pass. Keep in mind that viruses are generally smaller than 0.2 microns, and thus filters are not effective at getting rid of them.

In the past decade, the power of ultraviolet, or UV, light has been made portable and now is used to sterilize water by damaging the DNA of all microorganisms that can reside in water. When combined with a pre-filter that gets rids of larger sediment in the water, a portable UV device can quickly create drinking water on the go. The downside of these devices is that they require batteries, which might not be readily available in emergency situations or on post-apocalyptic earth.

Don’t Pass The Salt

Another rule to remember is never drink seawater. Doing so can be fatal. Normal seawater has four times more salt that your bodily fluids. Instead of hydrating your body, drinking seawater will actually cause severe dehydration, which will eventually cause brain and organ failure. If seawater is your only option, you can desalinate your water using a reverse osmosis device. There are a few portable reverse osmosis devices on the market, but the price tag on these can be steep. Most require electricity to pump water through membranes that leave the salt behind, but a few models are designed to use hand power. These desalinators require a lot of maintenance to work properly, so they are not ideal for long-term use. If you just happen to be one of those moonshine addicts previously mentioned, you can actually use your distillery equipment to desalinate seawater.

Early human settlements were built near drinkable water sources, but innovation and technology have allowed our species to live in places where water is limited. The growing human population forced clean water to become an important commodity, yet if our infrastructure were to break down, the difference between those who live and those who die might just be decided by who has access to clean water.

This article was originally published in the Winter 2016 issue of BALLISTIC™. Subscription is available in print and digital editions here.