It’s a topic many of us would rather avoid. With climate change news worsening, and dire speculations increasingly credible, it’s natural to feel like changing the channel. Extreme weather events are popping up in all kinds of formerly peaceful areas.

Big storms can render wells and public water supplies undrinkable, when runoff washes chemicals such as pesticides and solvents and even raw sewage from failed septic systems into aquifers. We needn’t look far for darker water-contamination fears, including oil spills, bioterrorism, or nuclear accident.

It’s time to face our worries and get prepared. We can walk ourselves through some worst-case-scenarios in our minds, and put together the necessary supplies to weather the storm — or whatever heads our way. Once our emergency kits are safely stowed and family disaster plans are in place, the monsters of “what if” have lost some of their terror. The foundation of every disaster plan is water, because water is the foundation to our very survival.

Flooding in Gatineau, Quebec, Canada. 2017.

Safe water, that is. Many a hurricane victim has faced the literal version of the proverb: water, water, everywhere, and not a drop to drink. Contaminated water can cause short-term life-threatening dehydration from vomiting and diarrhea, or long-term chronic disease due to chemical or bacterial toxins. North Americans take our exceptionally safe tap water for granted, but even here, communities can be taken by surprise by sudden “boil water advisories”, often the result of a broken water line causing possible influx of pathogens, or local flooding. Residents of Toledo were doubly confused last month, first by a warning of dangerous levels of microcystin, a toxin produced by algae and bacteria “blooms” that can cause serious liver damage: don’t boil your water, residents were told. Boiling will only concentrate the toxins through evaporation; reverse osmosis is the only treatment capable of removing microcystin. Days later, Toledo citizens were confusingly told to boil all water before drinking. Only later was it clarified that this boil advisory was unrelated to the microcystin event: a broken water main had raised concerns about possible bacterial influx.

In response to similar incidents, industrial disasters, and extreme weather events, trust in the public water supply is shaken. Individual household preparedness begins to make more sense than ever. When it comes to water, what is “prepared”? Ideally, it’s a combination of more than one safety net.

After natural disasters like Hurricane Sandy, water is the most urgent supply delivered by rescue workers.

After natural disasters like Hurricane Sandy, water is the most urgent supply delivered by rescue workers.

What types of contaminants am I likely to encounter in a disaster?


E. Coli crops up most often in North American news, but dysentery, Legionnaire’s Disease, typhoid, and cholera are all familiar diseases caused by water-borne bacteria. Current sanitation and water treatment standards protect us from many of them. These tiny bugs cause big problems if ingested in sufficient quantities. In an emergency, municipal water lines can be compromised or broken, causing sewage or storm runoff to mingle with treated drinking water. Flooding can lead to a variety of groundwater sources becoming compromised when rivers and septic systems are subject to unusual water level surges and mingling. Bacterial contamination is the single most common threat to both public and private water supplies, and its impacts are quick, disabling, and potentially deadly. Long and narrow, most bacteria range from 1-10 microns long and 0.2-1 micron wide. Many home technologies treat bacteria with ease, including mechanical and membrane filters, ultraviolet treatment, chemical disinfection and boiling. Filter pore size should be a maximum of 0.2 microns. If heavy contamination is suspected, a combination of chemicals, UV, or boiling plus filtering should be used.

Parasites and protozoa

Giardia, cryptosporidium, and amoebic dysentery are common water protozoa which cause disease. Like bacteria, many other protozoa are harmless to humans, though they can contribute an unpleasant odor to water. Disease-causing protozoa form protective cysts when they are not inside a host (such as us). These cysts are generally 2-50 microns in diameter: much larger than bacteria. To rid your water of protozoa, use any mechanical or membrane filter that excludes bacteria, in addition to UV, chemicals, and boiling. Non-protozoan parasites, such as intestinal worms and the snails which cause schistosomiasis, are even larger than cysts, so the same technology is effective.


Viruses — including those causing hepatitis, gastroenteritis, meningitis and even polio — can also be transmitted by water. Viruses are tiny: 0.004 to 0.1 micron in diameter! Viruses are also harder to detect with standard water testing. Fortunately, we are less likely to encounter widespread viral contamination in North America — though anywhere fecal coliform is a problem, viruses may be present. UV, boiling, and chlorine are all effective in reducing viruses to insignificant levels. Reverse osmosis systems can also be used where power and water pressure are reliable.

Organic chemicals

Ironically, some of the most hazardous compounds present in water are labeled “organic”: in this case, volatile organic compounds, or VOCs. VOCs include most benzene derivatives, as well as compounds based on methane and ethylene, and well known toxins such as MTBE and toluene. VOC contamination is often caused by heavy industry, but can also result from improper disposal of solvents and petrochemicals by individual consumers. In major storms, flood waters can cause large quantities of VOCs to wash from landfills, gas stations, dry-cleaners, or industrial areas— or even from private garages — into both public and private water supplies. Activated carbon and reverse osmosis can both reduce VOCs; boiling will also vaporize many VOCs which evaporate at a lower temperature than water (vent the steam outside).

Inorganic chemicals,

“Inorganic”, in this case, simply means these contaminants do not contain carbon. Heavy metals, chlorine, arsenic, and fluoride all fall into this category. While these are all common problems in drinking water, disaster scenarios are less likely to increase these particular elements. Have your tap water tested yearly to find out if you should take steps to reduce inorganic chemicals with a home filtration system: which system you need will depend upon your specific contaminants. Mechanical, membrane filters, or multi-stage systems are common choices for these chemicals.

Radioactive contaminants

Radionuclides have gained prominence in public fears and loom large in any disaster impacting a nuclear reactor, such as the Fukushima catastrophe. Certain radioactive elements, including radon, uranium, and radium are naturally present in some groundwater: your water test results will display any relevant numbers, and significant levels should be treated with reverse osmosis, ion exchange, or distillation. While large-scale radioactive disaster contamination is relatively unlikely, those who live in the shadow of nuclear generators should be ready to cope with radionuclides in their water.


Turbidity indicates the cloudiness of water: mud, organic matter, or various sediments may be present, particularly in storm conditions. Turbidity in itself may not be dangerous, however high turbidity is often associated with the presence of microorganisms, and it creates a challenge for water treatment. Treatments, such as UV, boiling, or chemicals, that aim to destroy microbes can be sabotaged by excess particulate matter. Turbid water should be passed first through a filter capable of reducing particles: simple carbon filters work well, as do mechanical and membrane filters. A secondary disinfecting treatment should follow to destroy remaining pathogens.

Types of Water Treatment and Filtration

Portable Filters


Portable supermarket filter pitchers like Brita or Pur won’t help with many pathogens or chemical contaminants; the filter rate is too fast and the barriers insufficient. They can improve the taste and appearance of water before or after disinfection by chemical treatment or boiling.

Mechanical Filters, including Ceramic and Sand

Sand filters are unique in utilizing a biological film (various bacteria, fungi, and protozoa) that live in the top layers of the sand. As the water passes slowly through, dissolved organic matter, including pathogens, is absorbed and metabolized by the organisms. A sand filter has the advantage of material simplicity and can be created as a DIY home project, however it needs to be continually used and maintained in order to support the health of the living systems that make it effective. It’s effective in reducing bacteria and protozoa and some industrial pollution, but is less thorough in virus reduction, and is unable to remove dissolved contaminants such as salts, arsenic and fluoride. Sand filters are not recommended for use with chlorinated tap water, as the chlorine will be harmful to the biological film, and in the initial set-up of the sand filter the water passing through needs to contain enough living organisms to create a healthy colony. Sand filtration is suitable for use in a rural area for untreated surface water where bacteria and protozoa are the primary concerns.

Ceramic filters use tiny pores in the solid filter material to reduce sediment and exclude many bacteria and protozoa; ceramic filters cannot remove dissolved chemicals on their own, and are not considered reliably effective against viruses.


Activated carbon bonds with some contaminants as the water passes through, reducing quantities of chemicals including chlorine, volatile organic compounds, pesticides and benzene. Carbon filters vary widely in effectiveness, with carbon blocks performing better than granulated carbon, and slower-flowing filters showing greater reductions than quick-flow models. These filters are known for improving the taste and odor of water, but cannot affect many inorganic pollutants such as arsenic, fluoride, hexavalent chromium, nitrate and perchlorate, and they are not considered effective on microorganisms. Carbon filters cannot serve as a stand-alone preparedness treatment, though they can provide a helpful pre- or post-treatment stage, reducing turbidity or improving taste.

Membrane Filtration, including Reverse Osmosis

All membrane systems involve forcing water through microscopic pores: depending on the size of the pores, various particles can either pass through or are flushed away in waste water. The pore size of ultrafiltration, one membrane technology, removes many pathogens but does not eliminate most chemicals. Reverse Osmosis (RO) systems rely on a thin film membrane which excludes all particles larger than 0.1 nanometer (a nanometer is one billionth of a meter). This results in an extremely pure standard of drinking water, effectively free from microbial and chemical pollution, as well as heavy metals and even radionuclides. The removal of all of these particles cannot be estimated at 100% due to the expectation of tiny imperfections in and around the membrane, but RO sets a high standard. Unfortunately, for disaster preparedness the benefits are offset by high system and installation costs, as well as requirements for electricity and water pressure, as well as a high ratio of waste water to purified water: at least four gallons go down the drain for every gallon of purified water.

Ion Exchange

An ion-exchange resin often takes the form of tiny, porous polymer beads. When water contacts this resin, certain ions are absorbed by the beads, and other ions are released. Ion exchange systems are often used for water softening rather than purification, as they can reduce positively charged ions but do not guarantee water safety.

Berkey Light
Ion exchange can provide an essential role in combination with other filtration mechanisms, adding up to a thorough and reliable disaster-worthy system. The Berkey Light provides a good example of a preparedness filter that can be used every day. Its included “Black Berkey” purification elements give this countertop system incorporate ion exchange technology as well as tiny-pore mechanical filtration similar to standard ceramic filters. The ion exchange allows the Berkey to exclude challenging contaminants such as fluoride, in addition to viruses, bacteria, VOCs, pesticides, solvents, and even algal toxins like microsystin. No electricity, fuel, or running water are required makes it portable as well.


Ultraviolet light (UV) disinfection excels at effectively reducing bacterial cysts, viruses, protozoa and parasites. This is a purely physical process in which the UV radiation attacks the cells’ DNA, destroying them or at the least rendering them unable to reproduce. No residue is left in the water: this is both desirable for drinking, and a drawback for water storage. Other inert contaminants such as heavy metals or chemical residues are unaffected by UV treatment. UV systems require electricity to operate, and their effectiveness is reduced as turbidity increases, making them unsuitable for purifying pond water or other brackish sources.


Distillation is the basic process of boiling water and collecting the condensed steam. This simple process makes consistently drinkable water from any source in an emergency, even swimming pools, ponds, or seawater. It removes a wide spectrum of contaminants including radioactive isotopes, toxic metals, and organic pathogens; however many synthetic chemicals, such as some pesticides, herbicides, VOCs and chloramines convert to vapor at a lower temperature than water and can remain in the distilled water.

Though electricity is not required, this process can be energy intensive, as a significant amount of fuel will be consumed to distill enough water for a family’s needs. An alternative approach is to harness the sun’s energy with a homemade solar distiller, or simply use your solar oven. The Survival Still Water Purifier and Desalinator is a lightweight portable unit that can utilize any heat source.


Multi-stage filters, as the name implies, use various technologies to progressively reduce contaminants through a gradated series of permeable barriers. Most of these systems are designed to hook up to your plumbing, either at a point of entry to the house, under the sink, or on the countertop such as this easily installed water filter. Multi-stage systems vary widely depending on their materials and specifications, but most are not considered true preparedness filters, as they rely on reliable running water.

Chemical Disinfection

This process requires no equipment, and a bottle of bleach will store indefinitely. Chlorine bleach is the most common and universally-accepted home chemical treatment for water. If you drink city tap water, chances are you’re already used to the smell and taste of chlorine disinfection! Every household should have a bottle of plain unscented bleach with no additives (5 to 6 percent sodium hypochlorite should be the only active ingredient). Have an eyedropper stored with the bleach: “one drop” is actually a scientifically standardized measurement unit, unlike “one teaspoon”. Pre-filter the water as specified above. Use 16 drops per gallon of water. Stir and let stand for 30 minutes. Check for chlorine smell; if there is no detectable “swimming pool” aroma, add another 16 drops, stir, and wait another 30 minutes. If at this point there is no chlorine smell, the water may be too dirty for treatment, and should be discarded. Post-treatment carbon filtration will reduce the chlorine greatly for immediate drinking: chlorine should not be removed from storage water until ready to use.

Some sources also recommend iodine tablets, or using liquid iodine from your medicine cabinet. Since iodine is not standardized as bleach often is, treatment quantities can vary. Be aware that sunlight can compromise iodine’s potency, and that some individuals have allergic reactions or health problems that may be impacted by iodine ingestion.


Back to basics: to kill pathogens, boil questionable water over a campfire or on any heat source. Most dissolved solids, toxins, and heavy metals, if present, will remain, though VOCs will be greatly reduced. However if you suspect microorganism contamination and have no other effective means of removing them, boiling can keep you from getting sick. The Red Cross actually recommends a combination of boiling for one minute, then treating with bleach. Other sources rely on boiling alone as sufficient, though some err on the side of caution, boiling for up to 10 minutes to be sure all pathogens are eliminated. First filter out any sediment or turbidity: simply pour through a coffee filter, paper towel, or clean t-shirt, changing the filter material whenever it begins to look dirty. Any particles in the water can provide a hiding place for bacteria, protecting them from the boiling water (this is the same reason you must always boil suspect water for the full time allotment before adding food for cooking). Pro: it’s simple, low-tech, and effective. Con: it requires fuel to achieve, which may be limited or unavailable in an emergency. If your stove requires electricity to operate, for instance, you should not make boiling fundamental to your water treatment plan.

Basic Water Survival Strategies

Bottled/Stored Water

We should all have a stash of safe water that needs no preparation. One gallon per person, per day is the rule — have enough for a minimum of three days. Store-bought bottles are simplest, as they are sealed and guaranteed drinkable through the expiry date (always keep track of that date and rotate your stock before it arrives). If you choose to store your own well or tap water, be aware it may need treatment (boiling or chemical) before drinking — some bacteria can survive even in treated water, and over long stretches of time in enclosed spaces these organisms can multiply to unsafe levels. For example, Legionella, the bacteria known to cause Legionnaire’s Disease, thrives during long storage, particularly at warm temperatures. Rotate every 6 months to be safe. For long-term storage, the EPA recommends 4-ppm chlorine: you can achieve this, if desired, with bleach and swimming pool test-strips. Sterilize and seal your food-grade containers. And in the short-term, remember to fill up your bathtub and large cooking pots at the first extreme weather warning. Supermarket bottled water stocks are often the first to sell out during storm warnings. Filtering stored water before use will improve both the taste and the purity.

Rainwater Catchment

Collecting your own rainwater provides a frequently renewed and rotated water storage system, and has the added benefit of reducing your water bill, or the demands on your well. Rainwater reduces overall household water needs, and is great for garden and landscape irrigation. In an emergency that keeps you at home for an extended period without running water, your rain barrels become a lifeline. If your system is kept clean and rotated, the resulting water can be consumed with only basic filtration. Unless local regulations prohibit rain barrels, many homeowners can install their own simple systems for up to 100 gallons of storage: enough to sustain a family of four for more than three weeks.


Before the advent of modern water treatment, many cultures avoided drinking water altogether in favor of processed liquids such as teas, beer, and wine (during the European settlement of North America, apple cider was an important staple). Before the germ theory of disease was widely accepted, folklore and superstitions against drinking plain water served as inherited protection. Times have changed: now, we can use easy home water test kits to provide immediate data on what we’re drinking.

With greater scientific understanding, our treatment choices have multiplied — unfortunately, so have possible contaminants. Choose a combination of emergency water options that feels right. Depending on your personal situation and your region, some approaches will make more sense than others. When an emergency strikes, you may be advised to boil or disinfect your water, or alternatively not to drink the water at all, turning instead to your stored water supply or distillation. If someone in your household has a weakened immune system, plan to use a combination-treatment approach — boiling and/or chemical treatment followed by filtering, for example. For healthy individuals, a single situationally-appropriate treatment may suffice; keep in mind that no tap water is sterile, and trace quantities of bacteria below certain thresholds are considered safe by the EPA.

Each home designs its emergency plan to match household members’ priorities, beliefs, and risk-tolerance. Apartment dwellers may have less storage space, making high-quality filtration even more important. A rural family with a large well or storage tanks may feel self-sufficient, but if forced to evacuate will need portable options. Weigh your needs and options, but don’t procrastinate: disasters don’t happen on schedule.

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