DISCLAIMER: This is a general overview and not a comprehensive guide to all waterborne contaminants and water purification methods. If you’re unsure if a source of water is safe, be sure to purify it thoroughly before using it for drinking, cooking, or cleaning.

Photos By: Amy Alton

Water. The source of all life, there’s no animal that isn’t composed partly of it. The microscopic tardigrade, also known as a “water bear,” can drop its moisture content to less than 1 percent of normal, but still harbors about 3 percent at its driest. Humans, however, are about 60 percent water and don’t have the ability to survive without fresh water for more than about three days.

In normal times, those who receive a water bill from their town or city are purchasing it from a system where the water is tested, and one that must prove to the Environmental Protection Agency (EPA) that it meets National Primary Drinking Standards. An annual water quality report is compiled and available through the water company with information about contaminants that have possible health effects. Having said that, germs and chemicals can get into the water, either at its source, through the distribution system, or even after leaving water treatment facilities. The Flint, Michigan, water crisis is one of the most infamous examples of this in recent history. The city’s drinking water was contaminated with harmful levels of lead, and studies also found evidence that an outbreak of Legionnaire’s disease (caused by waterborne bacteria) may have been linked to the municipal water supply.

Photo of water in a clear glass placed on a mossy rock.

Above: Clean drinking water is something we take for granted in modern society.

How Water Gets Contaminated

If water is taken from the wrong source, it can result in miserable illness or even death. The challenge is to find safe drinkable (potable) water or, at least, to have the materials and knowledge to make it safe to drink.

Harmful microorganisms or toxic chemicals can get in the water from many sources, including:

  • Fertilizers, pesticides, or other chemicals used on land near the water
  • Concentrated feed operations from livestock farms
  • Manufacturing operations from factories
  • Overflowing sewers and cracks in water piping systems
  • Flood waters
  • Wildlife (usually in smaller water sources like creeks)
  • Soil containing substances such as arsenic and uranium

Photo of brackish flood waters enveloping a suburban housing development.

Above: Flood waters aren’t safe to drink, as they often contain sewage and chemical runoff.

Safe to Drink or Not?

It’s not always obvious that water, even from the tap, is safe to drink. Some signs that should warn you of questionable water is if it’s:

Cloudy – Turbidity, or cloudiness, could signal the presence of disease-causing microbes.

Slimy – Hard water can cause your hands to feel slimy when touching it. This doesn’t have to mean danger but could indicate the presence of lead or other toxic metals.

Discolored – Brown or other colored water may signify the presence of microbes or toxins like copper, iron, or lead. It could also indicate tannins. Tannins are natural organic matter that can result from water passing through decaying vegetation. In small concentrations, they aren’t dangerous, but can cause a number of problems if present in excess.

Smelly – Water that smells bad could harbor disease-causing organisms or toxins like barium or cadmium. Odors like rotten eggs may indicate the presence of hydrogen sulfide. When exposed to certain bacteria, it converts into sulfate, which can cause dehydration or diarrhea.

A high level of suspicion is wise with just about any new water source. Even the clearest mountain stream may harbor giardia, a parasite that causes diarrhea and dehydration. Better safe than sorry.

If you lose access to municipal drinking water, you can still count certain sources in the home as generally safe:

  • Melted ice cubes made with water that isn’t contaminated
  • Liquid from canned vegetables and fruit
  • Water from your home’s toilet tank (not from the bowl), if it’s clear and not discolored by chemical treatment
  • Water from your home’s water heater (the tank that connects to the water that comes out of your faucets and showerheads)
  • Bottled water from coolers

Water from swimming pools and spas can be used for hygiene purposes, but not for drinking. Also, never use water from radiator tanks or boilers that are part of your home heating system. They are different from your water heater for faucets and showers and not safe to drink.

Photo of a latex gloved hand holding a a small beaker about to collect a sample of standing water.

Above: Water supplies are tested to see if they meet National Primary Drinking Standards.

Myths About Water Purification

  1. Water filters are expensive and high maintenance. Cheap water filters such as the Sawyer Mini, Lifestraw, and others are compact, lightweight, and easy to use.
  2. Bottled water is better. Bottled water is fine, but the quantity required for a family is huge over time and contributes to environmental damage. A water filtration system, on the other hand, is a one-time investment for continuous supplies of safe water.
  3. Water filters remove all the good minerals from your diet. Water filters do remove minerals, but the percentage of calcium, iron, and other minerals in water is small compared to what you get from food like vegetables, fruits, and leafy greens.
  4. Your city or town guarantees the supply of pure water. Municipalities use a lot of chemicals to make water safe for consumption; contaminants may always be present.
  5. Clear water and/or fast-flowing water is safe water. Pesticides, chemicals, microorganisms, and other contaminants that aren’t visible to the human eye may be present in tap water or naturally occurring sources.
  6. Water filters completely purify water. Water filters, well, filter, but they don’t always make water safe to drink. For example, a Lifestraw cannot remove the dissolved salt in seawater. Always consider the source of your water carefully and use a treatment method that’s suitable for the contaminants it might contain. To be extra safe, double-up with two purification methods.

Studio photo of a Lifestraw

Above: The Lifestraw, a compact, lightweight commercial water filter.

Disinfecting Water

If you suspect that the water quality is questionable, there are simple ways to help make it safe to drink. Boiling is perhaps the most well-known and eliminates bacteria, viruses, and parasites. Simply take a container, fill it with water, and get it to a rolling boil for one full minute. For altitudes over 6,500 feet, boil for three full minutes. Why? As altitude increases, the atmospheric pressure decreases as does the boiling point of water. To compensate for the lower boiling point, the boiling time must be increased.

Boiling takes fuel, so you might consider, instead, chemical disinfection to get rid of bacteria and viruses. This is most easily accomplished with 5 to 9 percent sodium hypochlorite (unscented household bleach). Use eight drops of bleach per gallon, but 16 drops if the water is cloudy. Mix the bleach into the water thoroughly, and let it stand for 30 minutes before consuming. Other chemicals such as iodine or chlorine dioxide will work as well after a period of waiting. Be aware that old bleach (older than six months) loses potency.

For storage purposes, calcium hypochlorite may be an improvement on household bleach. A 1-pound package of calcium hypochlorite in granular form can treat up to 10,000 gallons of drinking water. It destroys a variety of disease-causing organisms including bacteria, yeast, fungus, spores, and viruses.

Calcium hypochlorite is widely available for use as a swimming pool additive. Using granular calcium hypochlorite to disinfect water is a three-step process.

  1. To make a stock of chlorine solution (do not drink this!), dissolve one heaping teaspoon (about one-quarter of an ounce) of (78 percent) granular calcium hypochlorite for each 2 gallons (8 liters) of water.
  2. Add just one part of the chlorine solution to 100 parts water to be treated.
  3. Let the mixture sit for at least a half hour before drinking.

A photo of the top of a small container of partially dissolved calcium hypochlorite.

Above: Calcium hypochlorite can be stored as a solid water disinfection method.

In some circumstances, you may have neither fuel for boiling nor chemical agents for disinfection. In this case, you can use the ultraviolet light from the sun. This is known as the solar water disinfection (SODIS) method. Colorless, label-less 2-liter plastic or glass bottles will serve the purpose. Fill the bottle about 90 percent with the questionable but clear water. Then, expose it to full sunlight for six full hours. Cloudy weather takes much longer. If raining, collect the rainwater instead. For the best effect, consider placing the bottle on a reflective metal surface, such as aluminum foil, to increase the bottle’s light exposure. For a simpler way to UV sterilize water, there are commercial UV sterilizers available, such as the Steri-Pen.

It should be noted that water containing toxic chemicals or radioactivity is not made safe with any of the disinfection methods mentioned thus far.

A photo of a clear bottle filled with water resting on a sheet of aluminum foil in the sun as a water purification method.

Above: Ultraviolet light from full sun disinfects water in about 6 hours.

Common Waterborne Contaminants

Many bacteria, parasites, and viruses thrive in an aquatic environment, including:

  • Cryptosporidium
  • Legionella
  • Campylobacter
  • Norovirus
  • E. coli O157
  • Rotavirus
  • Enterovirus
  • Salmonella
  • Giardia
  • Shigella
  • Hepatitis A

Chemicals that have been known to contaminate tap water include:

  • Arsenic
  • Nitrate
  • Copper
  • Radon
  • Lead

Photo of the edge of murky, still water contaminated with litter.

Above: Questionable water sources require disinfection.

Filtering Water

You may have methods to disinfect water, but if it’s cloudy or has particulate matter in it, you must filter it first. Commercial filters such as the Lifestraw, Sawyer Mini, or the Berkey are useful and highly effective, but if you don’t have these, some improvisation is required.

Here’s a list of what you’ll need:

  • Plastic bottle with a cap
  • Knife
  • Hammer and nail
  • Coffee filter or thin cloth
  • Large cup or mug (either one works)
  • Activated charcoal
  • Sand
  • Gravel
  • Container to catch the water (jar, cup, mug, etc.)

Studio photo of a plastic bottle with a cap, a knife, hammer and nail, a coffee filter, activated charcoal, sand and gravel.

Above: Materials used to improvise a simple filter.

First, use the knife to cut the bottom off the plastic bottle. Take the hammer and nail and punch a hole or two in the cap. If you don’t have a hammer or nail, use the knife to cut an X shape into the bottle cap.

Photo of a someone cutting the conical part off of a clear plastic soda bottle.

Above: Cut off the bottom third of a clear plastic bottle.

Photo of someone using a hammer and nail to punch several holes into the top of a plastic soda bottle cap.

Above: Make one or two holes in the bottle cap.

Cover the mouth of the bottle with the coffee filter and tighten the cap over it. Put the bottle upside-down into the container that’ll collect the water (or use the cutout bottom of the bottle). 

Photo of a coffee filter screwed into place on a plastic soda bottle with the cap.

Above: Place the coffee filter or thin cloth between the bottle and the cap.

Now add layers of filtering material. Start by filling the bottom of the bottle with the charcoal. If the charcoal is in large pieces, break it down with the hammer into pea-sized particles.

Photo of an upside down, clear plastic soda bottle filled partially with activated charcoal.

Above: Place a layer of charcoal in the upside-down bottle.

Fill the middle with undyed sand.

Photo of an upside down, clear plastic soda bottle with a layer of activated charcoal on the bottom, and a layer of undyed sand on the top.

Above: Add a layer of loose sand.

Fill the rest with gravel (layers should be about the same thickness) but leave an inch or so of space at the top to avoid spillage.

Photo of an upside down, clear plastic soda bottle filled with a bottom layer of activated charcoal, a middle layer of undyed sand, and a top layer of loose gravel.

Above: Add a layer of gravel or small rocks.

The gravel layer will catch larger pieces of debris. The sand layer catches smaller particles, such as dirt, and the charcoal layer can reduce levels of bacteria and some chemicals. Be aware that, at the beginning, the charcoal may have some “soot.”

Photo of an improvised soda bottle water filter resting in a container to capture filtered water.

Above: Pour water to be filtered on top, let drain into container at bottom.

Hold your improvised filter over a container. Pour water in slowly and be patient, as the now-filtered water may take some time to flow into the container. If still not clear, put the water through a second time. If it takes too long, use thinner layers. Additional graduated layers may be added as desired.

Photo of an improvised soda bottle water filter next to a measuring glass of murky water.

Above: The improvised filter manages to capture most of the murky particulate.

Another method suggests making a filter out of the sapwood of trees like pine. Sapwood contains xylem, which filters out dirt and even bacteria (but not viruses). For this, you’ll begin with a plastic bottle as before. Then:

  • Cut a 4-inch-long piece from a pine tree branch of the thickness that, when the bark is peeled off, fits tightly into the bottle’s neck.
  • Slide the first inch or so of the stick into the neck of the bottle.
  • Cut the bottom of the bottle off and turn the bottle upside down.
  • Fill the bottle with water, and let the water drain through the stick.

With this method, it’s important that the xylem remains constantly moist, or you will lose the filtering effect.

While improvised water filters can greatly improve taste and odor as well as reduce levels of contaminants, it’s wise to follow up with a secondary purification method (such as bleach or boiling) whenever possible. Even if your DIY filter eliminates 90 percent of bacteria, the remaining 10 percent might still be enough to make you sick.

Photo of a pot of boiling water on a stove as a water purification method.

Above: Bring water to a rolling boil to disinfect it.

Storing Water Safely

Once you have a safe water source, you’ll want to store a supply of it. Use food-grade water storage containers; these won’t leach toxic substances into the water they’re holding and can be found at camping supply stores. The container you use should be made of durable materials; in other words, not glass. It should have a narrow opening that makes pouring easy and have a top that can be closed tightly. Avoid containers that previously held toxic chemicals, such as bleach. Write the date on a label and keep them stored in a dark place with a temperature preferably between 50 and 70 degrees F. Replace your water supply every six months or so.

Stored water will often taste “flat.”  This occurs because, over time, the water loses oxygen much like soda loses carbonation. To restore the original taste, shake your water in a container for a minute or two before drinking.

Studio photo of four blue water storage containers lined up left to right from shortest to tallest.

Above: Water storage containers must be food-grade quality.

What About Salt Water Purification Methods?

You’ve heard that it’s dangerous to drink salt water. Among other reasons, this is because:

  • The human kidney can’t eliminate large amounts of salt, causing excessive strain and leading to dehydration.
  • Too much salt causes elevated blood pressures that may lead to organ failure.
  • Drinking salt water causes muscle cramps.

Studio photo of the Sawyer Mini.

Above: The Lifestraw and Sawyer Mini are compact, lightweight commercial water filters. However, they cannot be used to desalinate seawater.

If your only option is salt water, there are ways to desalinate it. Off the grid, the best method may be distillation by evaporation. When water is evaporated, salt and other particles are separated from it. The distilled water is caught in a container and should be safe to drink. Desalination is most quickly achieved by boiling to trap steam; you can, however, get condensation from seawater with sunlight. You’ll need a pot, a smaller pot, some plastic wrap or sheeting, and one or two weights.

Partly fill the larger pot with sea water and put the smaller pot in the larger pot. Cover the whole thing with plastic wrap and put a weight on the plastic over the center of the smaller pot (but not touching it). Condensation of fresh water will occur on the inside of the plastic sheet, leaving the salt behind. The weight on the plastic will cause fresh water to drip into the smaller pot, which you can drink from. They call this method a “solar still” or “moisture trap.”

Photo of a solar still being used to distill salt water as a water purification method.

Above: An improvised solar still

About the Author

Joe Alton, MD, is a physician, medical preparedness advocate, and N.Y. Times-bestselling author of The Survival Medicine Handbook: The Essential Guide For When Help Is Not On The Way, now in its 700-page fourth edition. He’s also an outdoor enthusiast and member of The Wilderness Medical Society. His website at doomandbloom.net has over 1,300 articles, podcasts, and videos on medical preparedness as well as an entire line of quality medical kits designed by the author and packed in the United States.

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