How to Treat Water in the Backcountry

Clean drinking water is one of the 10 Essentials that you must always have with you or access to - no matter what.

You can’t survive for long without water, but drinking water directly from a stream or pond without treating it first can be a recipe for disaster.

Harmful, disease-causing “bugs” called pathogens contaminate virtually every untreated water source in the world, even pristine mountain streams deep in the wilderness.

You can easily ingest pathogens through drinking untreated water in the backcountry and become seriously ill as a result.

For this reason, it is extremely important that you always filter and/or purify your water before you drink it from a river, lake, or any other natural water source.

There are many way to treat water in the backcountry; so many that it is easy to become confused about the best method for your needs.

In this guide, you will learn the most important things you need to know about treating water in the backcountry, including how to choose a water filter or purifier, and the best practices to ensure that your drinking water is safe.

Table of Contents

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Why You Must Treat Your Water

Biologic contamination of fresh water is a widespread problem, even in the most remote wilderness areas of the United States.

No matter how clean and pristine a water source appears to be, you should always assume that it could be contaminated with dangerous microorganisms (tiny single celled organisms) and viruses.

Harmful microorganisms and viruses are called pathogens.

Pathogens can make you severely ill if ingested. For this reason, they are the main target for removal by backcountry water treatment systems.

Wildlife, livestock, and humans can all introduce pathogens into nearby water sources through feces and other waste.

The more heavily trafficked an area is, the more likely the water in that area will be contaminated.

Wilderness use is only increasing, and water sources in the backcountry are also increasing with biological contaminants.

Gastrointestinal infections cause by pathogens in backcountry water can cause significant fluid loss due to diarrhea and vomiting. In extreme cases, fluid loss can cause someone to go into hypovolemic shock, which is a life-threatening condition.

An infection from a pathogen can also cause you to develop flu-like symptoms that could debilitate you in the backcountry. This could lead to a serious emergency if you are not prepared.

While not every backcountry water source is contaminated with harmful pathogens, there is no way to know for sure if a water source is contaminated just by looking at it.

Pathogens are not visible to the naked eye because they are so small.

It is therefore critical that you always treat your drinking water in the backcountry - no matter what.

Before you learn how to do this, it is important to know about the harmful germs that you will be treating. This will help you choose the appropriate treatment system for your trip.

Bad Backcountry Germs

There are three main types of harmful pathogens that you should be aware of:

  • bacteria: single celled, simple organisms
  • protozoa: single celled organisms that are more complex than bacteria. Some form cysts that allow them to survive harsh environments, making them difficult to kill.
  • viruses: viruses are not living organisms but they are composed of organic molecules and have many similarities to living things (e.g. they have DNA)

There are several common bugs within each of these groups that pose the greatest threat to your health if you drink them in the backcountry.

Table 1 shows common pathogens within each of these three groups and their sizes.

Table 1. The most common pathogens you are likely to encounter in your water. Note: the width of a human hair is about 75-100 microns, for reference.

Hikers in North America generally only need to worry about bacteria and protozoa in their water, while those traveling in developing countries need to worry about bacteria, protozoa and viruses.

Other Water Contaminants

Unfortunately, pathogens aren’t the only things you have to worry about contaminating your water.

You will also want to treat or avoid:

  • Sediment/Turbidity: This occurs when water is cloudy or hazy due to silt, dirt, mud, plant matter, or other material that is suspended in the water. Turbid water doesn’t look “clean,” although it doesn’t necessarily contain pathogens. It can, however, upset your digestive system and reduced the effectiveness of certain water treatment systems.
  • Chemical pollutants: sadly, the wilderness can be contaminated with chemicals like pesticides, herbicides, and heavy metals from nearby human-related industrial operations like farming and mining. These typically can’t be removed with a backcountry water treatment system, so it's best to avoid them if possible. Do your research before you leave for your trip to ensure there is no serious chemical pollutants in the area.

The Two Main Types of Water Treatment Systems

In order to remove these pathogens from your backcountry drinking water, you will need use a reliable, effective water treatment system.

There are an almost dizzying number of ways to treat water in the backcountry these days, but they all fall into two general categories:

  1. Water Filters
  2. Water Purifiers
Water filtration and water purification are the two main ways to treat water in the backcountry.

The system you choose will depend on the type of pathogen or contaminant you are trying to remove from your water.

Water Purifiers vs Water Filters

The primary difference between a filter and a purifier is the type of pathogens each can remove from water.

Water filters only remove medium to large pathogens (bacteria and protozoa).

Water purifiers remove small, medium, and large pathogens (viruses, bacteria, and protozoa).

For this reason, I always use a water purifier when treating my water in the backcountry to ensure that it is as safe to drink as possible.

How Water Filters Work

Filters contain cartridges with microscopic pores that are permeable to water but not certain chemicals and pathogens.

The the size of the pores in a filter will determine what substances are allowed to pass through the filter.

Molecules or substances that are smaller than a filter’s pores will pass right through the filter.

Molecules or substances that are larger than a filters pores will get trapped in the filter and not pass through it.

This concept is illustrated in figure 1 below.

Figure 1. Illustration of how germs are filtered by pore size. Source: CDC

Water molecules are extremely small molecules relative to the size of most pathogens, so they easily pass through pores of a water filter.

When water is forced through a filter, pathogens in the water get trapped when they are too large to pass through the filter’s pores. This is shown on the left side of figure 1.

However, some pathogens, like viruses, are extremely small - small enough to pass through the pores of most water filters. This is shown on the right side of figure 1.

Water filters are rated in three different categories based on the size of pathogen that they filter out:

  • filter: only captures the largest particles: 1.0-4.0 microns in size (e.g. protozoa)
  • microfilter: captures medium to large particles: 0.2-1.0 microns in size (e.g. bacteria)
  • purifier - captures the smallest particles: 0.004 microns or larger in size (e.g. viruses)

If you are adventuring in an area where you know there will be viruses (e.g. a developing country), you will need a filter that is rated as a purifier. These filters contain pores small enough to filter out viruses.

Most water in the North American wilderness is free of pathogenic viruses, so microfilters are usually sufficient to filter out pathogens in this region.

How Water Purifiers Work

While some water filters can also act as purifiers (because they remove viruses), most water purifiers work entirely differently than water filters.

All pathogens are composed of organic and biological materials such as cells, DNA, and proteins.

Most purifiers destroy or “kill” pathogens by inhibiting or disrupting their biological activity (destroying cell membranes, denaturing DNA, etc.).

Pathogens can be destroyed when they are exposed to:

  • high heat (e.g. boiling water)
  • certain types of radiation (e.g. ultraviolet light)
  • certain chemicals (e.g. iodine or chlorine)

As you will learn in the water purification techniques below, these are three of the main techniques used to purify water in the backcountry.

Water Filtration Tools and Techniques

Pump Filters

Pump filters typically have an intake hose that draws water through the filter, and a pump that allows you to force water through the filter and out into a reservoir that collects the clean water.


  • They contain replaceable cartridges.
  • Intake hose usually makes it easier to access water from hard to reach water sources.


  • Expensive.
  • Large and heavy.
  • Pumping water can be tedious and tiresome.
  • Requires cleaning in the field.
  • They can break. All filters can break, but pump filters have more parts than other systems, which means they have more parts that are subject to failure.

Gravity Filters

Gravity filters work by using gravity to draw water through the filter rather than manually pumping or squeezing it through.

These filters include a reservoir that looks like a CamelBak or other similar water bladder which you fill with water and hang above the ground (e.g. from a tree branch).

Water then flows out from the bottom of the reservoir through a tube, eventually passing through the system’s filtration cartridge and into a reservoir that collects treated water.


  • The contain replaceable cartridges.
  • You don’t have to use effort to pump or squeeze water through the filter. The force of gravity draws water through for you.
  • You can relax or set up your camp while your water is filtering.
  • It’s the easiest way to treat lots of water - ideal when you are with a larger group or you want to collect a lot of water all at once.


  • Heavier than other options.
  • Slow.
  • Requires cleaning in the field.
  • It can be hard to fill the reservoir with water in shallow water sources.
  • Not ideal if you are camping above treeline and have no place to hang the water reservoir

Squeeze Filters

Squeeze filters are some of the simplest and lightest filters, making them very popular for hikers and backpackers.

These filters have two main components: a soft sided water reservoir (e.g a pouch or water bladder) and a filtration cartridge.

The cartridge attaches to the outside of the water reservoir.

All you have to do is fill up the water reservoir and squeeze the water through the cartridge. You can let the clean water flow into your water bottle before you drink it or, as with some squeeze filters like they , you can drink it directly as if you were drinking from a straw.


  • Very lightweight.
  • Contain replaceable cartridges.
  • Easy to use.
  • Relatively inexpensive.
  • Great for 1 person/solo water treatment.
  • Convenient - you can drink water almost immediately when you are at a water source.


  • Some are relatively slow and not practical if you are filtering lots of water at once.
  • You can only fill up a small amount of water at a time.
  • Requires cleaning in the field.

Bottle Filters

Like squeeze filters, bottle filters are also very simple and easy to use.

Bottle filters are essentially regular water bottles that contain some type of internal filtration system.

With most filter bottles, untreated water inside the bottle passes through a cartridge before it reaches the bottles drinking valve.


  • Lightweight.
  • Contain replaceable cartridges.
  • Easy to use.
  • Relatively inexpensive.
  • Convenient - you can drink water immediately or almost immediately after filling up.


  • Not practical if you are filtering lots of water at once.
  • You can only fill up a small amount of water at a time.
  • Slower flow rate than other filters.
  • Requires cleaning in the field.

Pro tip: a Sawyer Mini filter cartridge will fit on the opening of a SmartWater bottle, which you can find at any gas station or grocery store. This is one way to make your own filter bottle that is cheap and will fit into your pack’s water bottle side pocket. I also recommend checking out a company called CNOC Outdoors, which makes water reservoirs/bladders that fit onto Sawyer cartridges. In my opinion, these water bladders are way better than the ones that come with Sawyer water filters.

Straw Filters

Straw filters are perhaps the simplest filters out there.

Like the name suggests, you drink from these filters like a straw, directly from a water source.

The straw has an internal cartridge that filters water as you draw water through it.


  • Very lightweight.
  • Relatively small.
  • Relatively cheap.
  • Very easy to use.


  • You can’t collect water to drink later. You have to drink it directly from the source.
  • Only one person can drink from it at a time. Not a good solution for groups.
  • Cartridges can’t always be replaced.
  • It can be challenging to drink water directly from a hard to access source.

Filter Maintenance/Replacement

As you use a filter, particles that have been filtered out through the water treatment process will start to accumulate in the filter’s cartridge.

Everything from microscopic pathogens to larger particles such as sediment and algae will start to clog up the pores of the filter.

This will reduce the flow rate of the filter and potentially damage it, which is why filters need to be regularly maintained

Regular maintenance of a filter will not only ensure that your water is safe to drink, but it will also improve the performance and lifespan of your filter.

Every filter will have specific instructions provided by the manufacturer regarding how to maintain and clean your filter.

The most common way to clean a simple filter (e.g. a squeeze filter) is through a technique called backflushing or backwashing.

This is when you force clean water through the drinking side, or “clean” side of a filter towards the “dirty” side.

This flushes contaminants and debris out of the filter, restoring its flow rate and clearing out the filters pores. You can see an example of how to do this in a great video made by Sawyer here.

Other, more complex filters (e.g. pump filters) need to be taken apart. These filters have a more involved cleaning process that might not be desirable for you to do in the field, which is why many people prefer simple squeeze filters.

Again, closely follow the instructions for cleaning and maintenance that came with your filter. Most manufacturers have videos online that teach you how to clean your particular filter, too.

You should also take note of the lifespan of your filter, which total number of liters or gallons that your filter is capable of filtering until it needs to be replaced. Most filters aren’t guaranteed to last forever, so they need be replaced when they reach their lifespan (although some, like the Sawyer Mini squeeze filter, are supposed to last for 100,000 gallons, which you will probably never reach). Information about your filters lifespan will come with the filter.

Removing Unwanted Tastes: Activated Carbon

The water you drink in the backcountry can have a weird or  “earthy” taste, even if filtered properly.  

This is due to the fact that organic and inorganic substances like plant tannins and mud, can alter the chemical composition, and therefore taste, of water.

While these substances won’t necessarily hurt you if you ingest them, they can make water unpleasant to drink.

Filters often contain activated carbon, which is a highly porous substance that is effective at removing unwanted tastes and making water taste better.

Activated carbon has also been show to remove certain toxins and unwanted chemicals from water such as pesticides.

Look for a filter that contains activated carbon if you are interested if the taste of water is a concern for you.

Water Purification Tools and Techniques

If you are traveling to an area where there could be pathogenic viruses in the water (e.g. Hepatitis A), you will want to use a water purifier.

Remember, purifiers remove bacteria, protozoa, and viruses, while most filters (unless classified as purifiers), only remove bacteria and protozoa - not viruses.

Personally, I always use a purifier because I figure it’s better to be safe than sorry, even if the likelihood of there being harmful viruses in my water supply is very low.

Purification Filters

All of the water filters listed above come in variations classified as purifiers.

Only filters that are specifically rated as purifiers will remove viruses from your water. Filters rated as mirofilters or just filters will not.

Be sure to check that the water filter you choose is specifically rated as a “purifier” on the packaging by the manufacturer if you need to remove viruses from your water.

Chemical Purifiers

There are two types of chemicals that are typically used to purify water:

  • iodine
  • chlorine

Chemical purifiers come in the form of liquid drops or tablets that you drop into your water bottle and then allow to dissolve.

Depending on the type and specific brand of chemical treatment you buy, the instructions for use will be different. Follows these instructions exactly to ensure the treatment is effective.

Chemical purifiers usually make water taste awful. You can help improve the taste of chemically treated water by adding a small amount of vitamin C (~ 50 mg or so) or taste neutralizing tablets.

Important: when using chemical purifiers, be aware of:

  • The expiration date on the bottle. Don’t use expired chemical purifiers.
  • The amount of time the chemical is still “good” after opening the bottle. If you have an open bottle and can’t remember when it was opened, toss it out.
  • Not all chemical treatments kill 100% of all pathogens. Cryptosporidium in particular is hard to destroy, so not all chemical treatments are effective at killing it.
  • The cloudier the water is that you are treating, the more of a chemical purifier you will need to treat it. Cloudy (turbid) water reduces the effectiveness of chemical purifiers.
  • The colder the water you are treating, the less effective a chemical purifier will be. Try to warm your water before treating it, if possible, our double the treatment time if you have to treat very cold water.
  • The instructions - make sure you follow the instructions exactly and allow the appropriate amount of time for the chemical to treat your water before you drink it. this is usually at least 30 minutes.
  • Chemicals can be sensitive to light. Keep them in the dark bottles they came in so that they stay effective.
  • Chemical purifiers might not be safe for some people to drink. For example, if you are allergic to iodine or chlorine, you should not use this type of water treatment.


  • Extremely lightweight and small.
  • Relatively cheap.
  • Work as a good backup if your main water treatment methods fail.


  • Most taste bad.
  • Not an option for people who are allergic to iodine or chlorine.
  • You have to ingest a chemical - while these chemicals aren’t toxic for most people in small does, you might not be a fan of ingesting any “unnecessary” chemicals.
  • Doesn't remove “floaties” from water (e.g. dirt, algae or plant material that is harmless but unpleasant to drink).
  • Not all kill Cryptosporidium.
  • They expire.
  • Slow - you have to wait at least 30 minutes to drink your water. Sometimes you will have to wait many hours.
  • Not effective in cold water.
  • Doesn’t remove chemical contaminants like pesticides.

Ultraviolet Light Purification

Ultraviolet (UV) light is a form of radiation that is effective at destroying pathogens.

UV purifiers expose your water to UV light in order to purify it.

The most popular UV purifiers look like pens that you would write with. One of the most popular (and my personal favorite way to treat water) is called the SteriPen.

To use this type of purifier, you simply turn the purifier on, dip it into your water bottle, and then wait about a minute while your water is purified by UV light emitted by the purifier.

The purifier will have a timer that tells you when to remove the device from your water. Once the timer is up, your water is ready to drink.

Important: when using UV light purifiers, be aware of:

  • UV purifiers are less effective in cloudy, turbid water. Make sure that you prefilter your water before you use a UV purifier to treat your water (see above), or else it might not kill all of the pathogens in it.
  • The battery can die, leaving you without a purifier if you don’t have a way to recharge it (e.g. portable charger or solar charger) or a backup purifier.


  • They don’t require field cleaning.
  • Easy to use.
  • Lightweight.
  • Can treat a full Nalgene (1 liter) in less than a minute. Great for one or two people.
  • Devices with rechargeable batteries (like the SteriPen) can be recharged in the field with a portable charger and/or solar charger.


  • They have batteries that need to be charged in order to work.
  • Cold weather can drain battery quickly.
  • Not effective in turbid (cloudy) water.
  • Not ideal for treating lots of water for a group of people.
  • Doesn’t remove “floaties” from water.
  • Doesn’t remove chemical contaminants.


Boiling water is the surest way to kill all pathogens in your water.

Most microorganisms and viruses cannot survive in temperatures that reach 212 degrees Fahrenheit, the boiling point of water.

Boiling is just as effective at higher altitudes where the boiling temperature is slightly lower.

If you are ever in an emergency situation where you aren’t able to treat water (e.g. your main treatment system breaks), you can always make your water safe by boiling it if you have your camp stove on you.

In order to purify water through boiling:

  1. Bring a pot of water to a rolling. You should see large, fast-moving rolling bubbles emerging from the bottom of the pot.
  2. Cover the pot and let the water boil for at least 1 minute.
  3. Turn off the heat and allow the water to cool before using it to drink.

Important: always carry all of the tools you need to boil water if you plan on using this as a primary or backup method of treating water. Such tools include:

  • plenty of fuel - one 100 gram fuel canister should have enough fuel to boil about 10-12 liters of water, but factors like wind, temperature, elevation, and water temperature can affect the burn time.
  • stove
  • lighter - carry at least one extra lighters; stove igniters can break, so don’t rely on them.
  • metal pot


  • Can be very fast way to purify water for 1 person - especially with a Jetboil (see below).
  • If you are backpacking with a camp stove, you only have to bring extra fuel.
  • Prefiltering water isn’t required (but recommended) - boiling purifies tubid water just as effectively as clear water


  • Doesn’t remove “floaties” or chemical contaminants like pesticides and heavy metals.
  • You can’t quickly purify lots of water. Not a good solution for groups.
  • Carrying a stove and enough extra fuel is heavy.
  • You have to wait for water to cool before drinking.

Pro tip: If you are cold in your sleeping bag at night, fill up a Nalgene water bottle with boiling water. Then put the hot Nalgene in your sleeping bag. Not only will you stay warm in your sleeping bag, but you will also have sterilized water to drink in the morning when you wake up.

The Best System to Boil Water in the Backcountry

In my experience, the best way to boil water in the backcountry is to use the Jetboil Cooking System.

Jetboil makes awesome lightweight camp stoves that include all of the tools you need (except for fuel) to boil water.

Some models boil water in less than 2 minutes, which is crazy fast.

I always have one in my pack - mostly because I always need hot coffee. :)

A Jetboil can serve as a great backup to purify water if your main treatment method fails because it is light, efficient and effective.

How to Choose a Backcountry Water Treatment System

With so many different systems to treat water in the backcountry, how do you know which one is the best for you?

There is no simple answer for this since very trip you take will be different, and certain systems will be better for some trips and worse for others.

The system you choose as “best” will depend on many factors such as:

  • Where you will be traveling.
  • How many people will be on your trip and how much water you will need to purify.
  • Whether or not you need to purify your water for viruses or just filter it for bacteria and protozoa.
  • The quality of water you will be near (e.g. clear high alpine streams or silty puddles in the desert).
  • Whether or not you will be in freezing weather.
  • The weight you are willing to carry.
  • How quickly you will want to treat your water.
  • Allergies that you our anyone in your group might have to chemical purifiers.
  • Other personal preferences like how you want your water to taste and look (e.g. can you handle “floaties” in you water or do you mind chemical tastes?).

To simplify this decision making process, I have put together a flow chart that will help choose the best water treatment system for your particular needs.

Always prioritize water safety over anything else.

This means first deciding if you need a purifier or a filter.

Do you research and make sure that the treatment system you choose will remove all of the pathogens that could potentially be in your water.

For example, if you plan on traveling in a developing country, you will need a purifier that removes viruses. However, if you are backpacking through remote alpine wilderness areas in the United States, you probably won’t have to worry about viruses and you will only need a filter.

Once you decide if you need a purifier or a filter, then you can start weighing the pros and cons of each system based on the type of trip you plan on taking.

Everyone is different in terms of their personal preferences. Get clear about what you prefer (e.g. do you prefer low weight? fast speed? taste?), and this will help you decide on the best system for you.

What I Use Most of the Time and Why

I live in Colorado, so most of my hiking and backpacking is done in alpine wilderness environments where there is an abundant source of water from clear rivers and streams.

This water is usually:

  • clear
  • flowing
  • unlikely to have been in significant contact with humans, livestock, or industrial activities
  • from snowmelt

These factors mean that the water is likely low in pathogens and other harmful contaminants. It still must be treated though, because there is no way to know if it’s truly safe.

During the warmer months, I treat water with a Sawyer Mini squeeze filter AND a SteriPen UV light purifier.

I love the Sawyer Mini filter because:

  • It is extremely light.
  • It filters water fast enough for one person (most of my backpacking/hiking is done solo or with 1-2 other people).
  • It’s easy to use.
  • It will last an extremely long time before needing to be replaced.
  • It requires only a small amount of maintenance when filling up fresh, clear mountain water.

Theoretically, filtering my water with the Sawyer Mini squeeze filter should be enough to make it safe because it is highly unlikely that there are pathogenic viruses in the water in the Colorado alpine wilderness.

However, I always use the SteriPen in conjunction with the Sawyer Mini because:

  • It adds extra insurance - if something got through the filter, the SteriPen should purify the remaining bugs.
  • It’s a great backup in case the Sawyer Mini breaks or fails.
  • Since the water I treat is usually clear, the UV light is highly effective.

This setup has worked very well for me and I highly recommend it if you only need to filter water for 1-2 people in an area that has relatively clean water.

How To Know if Your Water is Safe to Drink

The ingestion of pathogens - even a very small amount - poses a significant, immediate threat to your health and safety while out adventuring in the wilderness.

When all pathogens have been removed from your water, either through filtration, purification, or a combination of the two, your water can be considered safe to drink for the duration of your trip.

Non-biological contaminants like heavy metals, pesticides, and herbicides pose little threat in the short because they slowly accumulate in your body and usually require high levels of repeated exposure to make you sick. These contaminants are something you shouldn’t need to worry about when treating water in in well managed North American wilderness areas.

Unfortunately, there is no way to know for sure if your water is free of pathogens after you treat it in the backcountry.

Water filters are not regulated by the government, and there is no regulatory agency or certification that ensures that a treatment systems upholds the manufacturers claims.

I recommend a few guidelines to ensure that your water is safe to drink (i.e. free of pathogens) in the backcountry:

  • Choose a water treatment system from a reputable company, preferably one that has done third party independent lab testing to prove that their system meets or exceeds Environmental Protection Agency (EPA) standards. Example of such companies include Sawyer, MSR, and LifeStraw.
  • Always follow the exact instructions that your system came with.
  • Regularly maintain your treatment system if necessary (e.g. filters need to be regularly cleaned - see above).
  • Aim to be 100% certain that your system has not been damaged or compromised in any way before using it. For example, if you have a filter that froze or was dropped, consider using your backup treatment method instead (see below).
  • Use two systems together every time you treat water for extra “insurance.” For example, I filter my water and purify it with a SteriPen using UV light.
  • Do your research and be observant of your surroundings so you know what contaminants could potentially be in your water. This way you will know that you are treating your water for the contaminants you know you need to remove. If you will be in an area where there could potentially be viruses (e.g. if you are traveling in the developing world), then you will definitely need to purify your water.

Emergency Backups

Given the importance of clean, safe drinking water in the backcountry, it is critical that you always have a backup water treatment system.

All water filters and purifiers have the potential to break.

If your water treatment system malfunctions in the backcountry and you don’t have a backup, you could get seriously ill if you are forced to drink untreated water.

After you decide on your primary water treatment method, you should seriously consider what you will carry as a backup.

The best water treatment backups are extremely light, relatively cheap, and/or already in your bag.

Great emergency backup options include:

Where and How to Collect Water in the Backcountry

When you are out on a trip in the wilderness, you may or may not have the luxury to choose where to fill up your water.

If you do have a choice, it is important to know that some water sources are considered better quality than others.

A quality water source is one that is likely to have lower levels of pathogens and contaminants like silt and algae.

Try to filter the cleanest water you can find.

This way you can avoid clogging your filter and the other issues with turbidity described above.

Where to Find a Quality Water Source

Here’s what to look for:

  • Running water: the best sources of water are rivers and streams. Microorganisms do not thrive in flowing water.
  • Clear water: this may seem obvious, but water that is cloudy likely contains sediment and organic matter that affect the effectiveness of your water treatment method.
  • Calm water: sediment and other debris is more likely to settle to the bottom of a water source when it is calm.

Here’s what to avoid:

  • Puddles or shallow or other standing water sources.
  • Cloudy, turbid water that contains algae blooms, sediment, or other visible solids. If you need to treat water like this, you may want to use a prefilter firstt.
  • Water near animal pastures or areas with obvious signs of animal traffic or habitation.
  • Water with dead fish or other dead organisms. This could be a sign of toxic water.

How to Collect Water

It is a best practice to collect water from the surface of the water source you choose.

Surface water is usually the clearest and of the highest quality.

If your only water source is full of sediment or other visible contaminants, you can:

  • Fill up a pot or bag with water and let it sit until the solids have settled to the bottom. Then you can collect the clearest water at the surface.
  • Use a prefilter to remove excess sediment and debris. Silt, mud, leaves, and other “floaties” in cloudy water can interfere with your water filter and the effectiveness of chemical treatments.

Important: make sure you keep dirty and clean water reservoirs separated, and avoid contaminating the threads of your drinking reservoir (e.g your water bottle) with contaminated water.

  • Any container that has touched dirty water (e.g. lake, river, pond, stream water, etc.) should be considered contaminated with pathogens.
  • If a water container was accidentally filled with untreated water from he backcountry, it should be cleaned before filling it with clean, treated water.
  • If the threads or mouth of your water bottle have come in contact with untreated water (e.g. you dipped the bottle in a river before sterilizing the water inside), you should not drink from it until you have rinsed the threads with clean, treated water. A simple way to clean the threads are to turn your bottle upside down, loosen the cap, and let clean, treated water run through.

How to Collect, Purify, and Store Water in Freezing Weather

If you are adventuring in blow freezing conditions, special considerations must be made regarding how you should treat your water for pathogens.

In many wilderness areas, the most abundant source of water in the winter is stored as snow, which can be melted and then purified into drinking water.

Photo credit: Simon Berger on Unsplash

Clean, fresh snow is usually free of most pathogens, but it’s never guaranteed to be completely safe to drink when melted.

Never melt and drink dirty snow. Melt it and then purify it

Your best option for treating water in freezing cold environments is usually to boil cold water, ice, or snow.

To melt snow:

  1. Fire up your stove and pour some water into your pot.
  2. Heat up the water on your stove. Add some nearby snow to the pot.
  3. Slowly keep adding snow as it melts. You will need about 10 liters of snow to make 1 liter of water.
  4. Once you have collected the water you need, either bring it to a boil for at least a minute to purify, or treat warm water with chemical purifiers or UV light.

Other filtration and purification methods are difficult or impossible to use for the following reasons:

  • Filtration: water can freeze inside of a filter, making it impossible to operate. Filters can also break in freezing temperatures because when water turns to ice, it expands. This can crack your filter and create leaks through which pathogens can pass.
  • Chemical purification: chemical purifiers lose their effectiveness in cold weather. Only use chemical purification if you can warm your water up to at least 60 degrees Fahrenheit first.
  • UV light: batteries lose their charge faster in cold weather. this goes for all batteries in any electronic device. UV pens can be an option in cold weather to treat melted snow, but take into consideration that it might run out of batteries more quickly.

Important: do not eat snow. This will lower your body temperature and could potentially make you hypothermic. Your body has to use a lot of energy to convert water from snow to a liquid, and you will waste valuable calories in the process. You would also have to eat a lot of snow in order to get a relatively small amount of water in your body. Also, if you eat “dirty” snow, you could potentially ingest pathogens since the snow hasn’t been purified.

How to Prevent Your Water from Freezing

Even after you collect and treat water properly in the wintertime, you still have to deal with it freezing or re-freezing.

Here are a few tips to prevent your water from freezing on a winter hike or backpacking trip:

  • Use water bottles that have wide mouths. The opening of wide mouth water bottles don’t freeze as quickly as small mouthed ones.
  • Carry your water bottle upside down. The top of the bottle freezes first, so this will delay the freezing of opening.
  • Purchase a water bottle insulator like this, or consider carrying an insulated bottle such as a Hydro Flask (even though they are heavy, they will keep your water warm and prevent it from freezing for a very long time).
  • If you use a water bladder system like a CamelBak, use a hydration tube insulation sleeve like this one. The tubes freeze quite quickly. Some insulators are designed to replace the tube that the bladder came with, and some can be used on your existing tube.
  • Keep you water bottles in your sleeping bag at night.

Pro tip: If you use a UV purifier pen like a SteriPen, keep it in a pocket close to your body and sleep with it in your sleeping bag. This will keep the battery warm and prevent it from draining as quickly. This also goes for other batteries you might need like your camera batteries!

Water Treatment Best Practices Summary

  • Always have a backup water treatment system (or two).
  • Follow the instructions provided by your water treatment system’s manufacturer.
  • Keep dirty and clean water reservoirs separate.
  • Be careful to avoid contaminating the threads of your water bottle with untreated water. Clean or rinse the threads before drinking from your water bottle.
  • Fill up from clear, quality water sources if possible.
  • Regular maintenance of a filter will not only ensure that your water is safe to drink, but it will also improve the performance and lifespan of your filter.
  • Prefilter turbid, cloudy water before treating, especially if you plan on using a SteriPEN or chemical purifiers.
  • Boiling cold water or snow is usually the best way to purify water in freezing temperatures.

Prefilters: Treat Turbid Water Before Filtration or Purification

If you are in a situation where you have to treat turbid water (i.e. cloudy or opaque water), it is a good idea to use a prefilter to remove the contaminants that are clouding it up (e.g. silt, mud, algae).

Prefilters are used before you filter or purify water for pathogens using the filtration and purification techniques listed below.

A prefilter alone will not make your water safe to drink.

The higher the turbidity of a water source, the murkier it will be, and the more necessary it will be to use a prefilter.

A prefilter is important for the following reasons:

  • It will extend the life of your water filters and and reduce the amount of maintenance/cleaning they require. Sediment and other suspended solids in turbid water can clog up water filters if water is not prefiltered first.
  • It helps ensure that your water purification treatment is working. The effectiveness of certain purifiers (e.g. UV light and chemical treatments like iodine) decreases as water turbidity increases.
  • It reduces the growth of pathogens in your water. The higher the turbidity of water, the more likely it is to contain dangerous pathogens because the suspended particles in turbid water provide food and shelter for them.

How to Prefilter Your Water

Prefilters are often built into a water filters to prevent them from clogging, so you might not need to worry about prefifltering water if your treatment system already has one.

Other prefilters are sold and carried separately. My current favorite backpacking prefilter is the SteriPen FitsAll Filter.

You can also strain water through a cloth or bandana if you find yourself without a prefilter when you need one.