How To Purify Water When Backpacking

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How Much Water Do I Need Take Backpacking

As a general rule of thumb, you need to drink about a half-liter of water every hour while hiking. In other words, your body needs 3 to 5 liters per day when backpacking. If breathing heavily and sweating profusely, you may end up needing to drink a liter of water or more per hour.

What Are Water Sources Along The Trail

mountain stream with waterfall and trees with fall colored leaves.

You often need to replenish or purify your water supply when hiking or backpacking. How do you resupply water during extended wilderness adventures? You cannot run to the kitchen faucet and refill your water bottles. Therefore you have to rely on water sources found along the trail.

As a result of seasonality or your trail itinerary, water may not always be available. Desert hikes may have limited or nonexistent water supplies. Streams may be dry. Most importantly, make sure you carry enough water with you in your daypack or backpack. In addition, check the availability of water along the trail before you set out.

Rivers, streams, and lakes are one source for replenishing your water supply. Also, natural springs can sometimes be found along trails. In addition, vernal pools and rock depressions in desert regions hold water for a short time after recent rains.

Most importantly, is the water you find safe to drink? Does it need to be filtered or purified? You trust the municipal water supply at home. But how do you trust water supplies while backpacking?

Always Purify Water When Backpacking

stream with waste and debris that show why you need to purify water when hiking


As a teenager in the 1960s, we drank right out of the streams. The Sierra Nevada Mountains had crystal clear pristine lakes and streams. Even in the 1970s when I started backpacking in earnest I never filtered my water. In fact, I didn’t know anyone who did. But now, those days are long gone.

My parents hosted a foreign exchange student from Switzerland in the mid-1970s. I took her and my sister backpacking in Yosemite. Judy could not get over the fact that we drank right from the streams. She said the water in Switzerland was not safe to drink without filtering or using purification tablets, that was the first time I was introduced to the idea that I needed to purify water when backpacking!

Today it is no longer considered safe to drink water that has not been filtered, boiled, or chemically purified. Micro-organisms and water pollution are more prevalent in today’s world, therefore making water filtration a requirement.

The sad reality of aging is you become more susceptible to disease and infection than when younger. As a result, clean drinking water is more important as we age. Especially as senior hikers, we need to purify our water when backpacking to keep us safe on the trail.

Why Is Water Filtered Or Purified When Backpacking

man with backpack drinking water from a mountain lake. 

Clean drinking water is necessary, our health depends on it! However, water sources in wilderness settings may be polluted. For instance, pack animals and grazing cattle leave fecal matter on the ground near water sources. In addition, cat holes dug by hikers and backpackers today are often too close to water sources. Even past mining operations and ore tailings can affect water quality.

So, what pollutants do hikers and backpackers have to worry about? Here is a list of the most common:

  • Protozoans    
  • Bacteria      
  • Viruses    
  • Volatile Organic Compounds (VOCs)      
  • Heavy Metals
  • Mining Toxic Waste

Protozoans are microscopic parasites such as Giardia and Cryptosporidium protozoa represent one type of drinking water contamination. These creatures live in soil, water, and in the intestines of humans and other mammals. Water becomes contaminated when it comes into contact with sewage and animal waste.         

Cryptosporidium parvum is responsible for cryptosporidiosis. This causes symptoms such as fever, headache, vomiting, nausea, cramps, and diarrhea. Usually, the symptoms subside after a week and rarely last longer than two weeks.      

Giardia lamblia causes giardiasis. Known symptoms are diarrhea, cramps, nausea, general intestinal distress, and weight loss. Sometimes dehydration and nutritional loss may need immediate treatment. The symptoms begin within the first week of exposure. These symptoms rarely last longer than two weeks. Fortunately, giardiasis seldom results in anything serious.

Bacteria are common single-celled organisms.  They are a natural component of lakes, rivers, and streams. Most of these bacteria are harmless to humans. However, certain bacteria have the potential to cause sickness and disease in humans.

Escherichia coli (E. coli) bacteria are found in the environment. The bacteria are most often associated with contaminated foods. However, it lives in the intestines of people and animals as well.  Although most strains of E. coli are harmless, others make you sick. 

Water contaminated with the feces of domestic and wild animals can cause a variety of illnesses. Minor gastrointestinal discomfort is probably the most common symptom. However, what may cause only minor sickness in some people may cause serious illness or death in others. This is especially true in the very young, old, or those with weakened immune systems.


The U.S. Environmental Protection Agency (USEPA) regulates the testing of drinking water for adenovirus, caliciviruses, enteroviruses, and hepatitis A, and most recently Covid-19 for potential regulatory action. The current US regulations require the removal or inactivation of 99.99% of enteric viruses. Water sources found in wilderness settings are not evaluated for contamination.

Volatile Organic Compounds (VOCs)   

VOCs are a wide group of chemicals. They evaporate easily at room temperature. Common sources of VOCs include paints, varnishes, cleaning products, pesticides, adhesives, etc. 

In addition, hydrocarbon pollutants from the burning of gasoline, wood, and other petroleum-based fuels contribute to water pollution.           


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Heavy Metals

Heavy Metals come from natural formations in the Earth’s crust. They are named so because of their high molecular density. Some of the most common ones are iron, tin, gold, copper, and silver. Many of these metals are essential to human bodily functions. Others, such as arsenic, cadmium, mercury, and lead are highly poisonous. There are several heavy metals identified by the World Health Organization (WHO) which can pollute water sources. They include lead, cadmium, mercury, and arsenic.

Mining Toxic Waste

Every day many millions of gallons of water laced with arsenic, sulphuric acid, lead, and other toxic metals flow from some of the most contaminated mining sites in the United States. Hence, that water flows into surrounding streams and ponds without being treated. It is poisoning aquatic life and tainting water supplies in Montana, California, Colorado, Oklahoma, and at least five other states.

In addition, even extremely remote areas may have had mining operations in the past. The Geez was backpacking in the Grand Canyon several years ago. The backcountry office cautioned against drinking water from Horn Creek because of radioactive contamination. In short, always check water sources before outdoor adventures. As an example, here is a list of all of the water sources along trails in the Grand Canyon. Most are safe to drink but some are not.

What Do I Use To Purify Water When Backpacking

man showing how to purify water at a lake in the mountains

There are many ways to make sure your water is safe to drink. The following list covers the most popular methods.

  1. Natural Alternatives
  2. Chemical Treatments
  3. Water Filtering
  4. Heat
  5. UV Light

1. How To Purify Water With Natural Alternatives

Natural spring water, welling up from deep underground, is one source of clean drinking water. It is often commercially bottled and sold in stores across the nation. Some natural springs can be found along hiking trails. For instance, I day hiked to Mt. Whitney several years ago. We refilled our water bottles from a natural spring along the way.

To be clear, natural spring water is usually safe to drink. But it is always advisable to research water sources before hiking. You never know, even spring water may be contaminated because of prior or ongoing mining and fracking operations.

But what about stream water? Is it contaminated and should you worry about drinking it. In other words, should you worry about waterborne pathogens in stream water? To be clear, Giardia or Cryptosporidium may indeed be present in the water. But are they prevalent in sufficient quantities to cause infection?

What About Bacteria In The Water

A 1993 research study took a look at Giardia infections and gastrointestinal illnesses in backcountry travelers. This study was done in high-use areas of California’s Sierra Nevada Mountains. That study failed to find any significant link between wilderness water consumption and infection from these threats.

Additional studies have sampled water sources near sites with heavy human and pack animal traffic. As with Giardia and Cryptosporidium, the concentrations of fecal coliform bacteria were so low as to be barely detectable. In addition, a study from Backpacker Magazine found pathogens in only a few selected sites. The concentration of pathogens was so low it would take drinking 7 liters of water at one time to potentially get sick.

In short, you probably don’t need to filter or purify stream water when backpacking. Even if bacteria or parasites are present, ultraviolet light from the sun effectively lowers pathogen concentrations.  However, it is likely most outdoor enthusiasts will continue to filter or purify their water. The perceived risk warrants treating your water out of an abundance of caution.

2. How To Purify Water With Chemical Treatments

The use of chemicals to treat water has a long-standing history. Most municipal water supplies are treated with chemicals. Hikers and backpackers can use them to purify their drinking water. There are several water treatment options available.

Chlorine Dioxide is one water treatment option. As an EPA-registered biocide, chlorine dioxide is used to purify drinking water. It is effective against waterborne pathogenic agents such as viruses, bacteria, and protozoa. This includes both Giardia and Cryptosporidium.

Water purifying tablets containing the active ingredient Tetraglycine Hydroperiodide have been used by military and emergency organizations worldwide for over 50 years. They are ideal as backpacking water purification tablets.  They make questionable water bacteriologically suitable to drink within 35 minutes.

Yet another chemical water treatment is Sodium Dichloroisocyanurate. At a 17% concentration, each tablet creates 2.6ppm of available chlorine when dissolved in 2 liters of water.  Disinfected water is safe for drinking in as little as 30 minutes.

And lastly, Colloidal Silver can be used to purify water when backpacking. Silver is one of the oldest known antimicrobials. Colloidal silver has been proven in studies to eradicate over 650 different pathogens, including giardia. It inhibits the enzyme the parasite needs for oxygen metabolism, effectively suffocating it. Add a drop of 36ppm (parts per million) colloidal silver to a liter of water. Viruses and bacteria are eliminated within 30 minutes, making the water safe to drink.

3. How To Purify Water With Water Filtering

The purpose of a water filter is to filter out microscopic particles and parasites from your drinking water. The filter membrane stops them from flowing through with the clean water. A filter’s effectiveness is determined by the size of the openings in the membrane.

The size of the filter’s openings is measured in microns. One micron is equal to a thousandth of a millimeter. Any water filter with a size of one micron or less will remove parasite eggs and larvae from the water as well as protozoa. Hence, Giardia and Cryptos­poridium are removed. Bacteria removal requires a size of less than 0.4 microns.

Regardless of the type of water filter, they all work in the same basic way. Water is pushed through the filter, either manually for a freestanding filter, or through suction with a water bottle filter. Thus, any microorganisms that may be living in the water are trapped inside the filter. As the water flow rate decreases, the filter must be back-flushed to remove trapped dirt particles and microorganisms.

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3 Ways To Pressure Filter Water

The pressure required to push water through the filter is accomplished in three ways. The Sawyer Squeeze System includes a squeeze bag that connects to the inlet side of the filter. The bag with water is manually squeezed by hand. The Katadyn Hiker Pro uses a hand pump to push the water through the filter. The Katadyn BeFree water bottle and the LifeStraw personal water filter use your mouth to suck water through the filter. And finally, the Platypus GravityWorks uses the weight of the unfiltered water to push the water through the filter.

The Geez was a partner in an international import business a number of years ago. Our client database included several water filtration companies. 

Seychelle arguably makes the best water filter in the world. Using their proprietary Ionic Adsorption Micro-Filtration technology, the filter removes up to 99.99% of the contaminants and pollutants that can be found in drinking water. This filter is overkill in most instances. Most importantly, with it you can travel anywhere in the world and drink the local water.

4. How To Purify Water With Heat

Boiling is the surest method to kill disease-causing organisms. Heat completely avoids potentially harmful chemicals. Also, it does not alter the taste of your water. Boiling kills viruses, bacteria, and parasites.

To purify your water, bring it to a full rolling boil for 1 minute. At elevations above 6,500 feet, boil for 3 minutes. Afterward, allow the water to cool before use.

5. How To Purify Water With UV Light

Ultraviolet light kills microorganisms as well. Small handheld units like SteriPen Aqua UV Water Purifier are able to purify a liter of water in about 90 seconds. UV light destroys over 99.9% of harmful bacteria, viruses, and protozoa like Giardia and Cryptosporidium. An added benefit of UV devices is the weight. The SteriPen only weighs 2.93 ounces. It is small, lightweight, and does not take up much room in your backpack.

In Summary

Water treatment in the backcountry is a personal choice. If you trust the water source you may wish to forego treating the water. However, the risk of gastrointestinal sickness is real. You may not want to assume that risk.

There are several ways hikers and backpackers can be assured that their drinking water is safe. Choose the one most appropriate for you.

Be safe.

get over the hill the geez signature.


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