Getting reliable drinking water during outdoor adventures can be a tricky task. Even when you are surrounded by crystal clear lakes with no one around you, the water could be contaminated with harmful bacteria and viruses. When traveling in less developed countries, the chances are likely that also tap water is contaminated. Even when the water looks clear, that doesn’t mean it is clean.

There is a wide range of water treatment systems out there that are specifically developed for outdoor activities and traveling. They all have their own advantages and disadvantages. This article provides a complete overview of the different water treatment methods and when to use them.

water filters and water purifiers
filtering water on a bikepacking trip in Peru

Water filtration and water purification

Most people talk about water filters when talking about water treatment. But water treatment can be classified into water filters and water purifiers. They are two different things. In general, water filters remove particles and thereby protect against bacteria and protozoa (parasites). While water purifiers eliminate bacteria, protozoa ánd viruses. 

Water filters work by blocking the passage of particles, protozoa, and bacteria – basically anything larger than 2 microns. Water filters cannot remove viruses since viruses are too small (1000 times smaller than bacteria) and hence they can slip through the filters. Water purifiers use other techniques such as ultraviolet light, chemicals, heat or ultra-filtration to eliminate waterborne viruses.

Do I need a water filter or a water purifier for outdoor activities?

Which water treatment do you need, comes down to one question. Should you worry about the viruses in the water or not? In remote areas, for example, high up in the mountains, the risk that water is contaminated with harmful viruses is relatively low. How does that work? 

In general, protozoa and bacteria infect and affect both animals and humans alike. They are transmitted through water sources by human and animal waste. Animals and humans drinking from this source will both be infected with these protozoa and bacteria. In contrast, most viruses are species-specific. Therefore, most waterborne viruses that affect humans are transmitted by human waste alone. Not via animal waste.

As a rule of thumb, you could use the following: In remote areas with few people around, water requires filtration. There, the biggest concerns are ‘dirty’ water (silt and debris), bacteria and protozoa, and not so much viruses. 

Traveling in less developed countries with poor sanitation, the chances that tapwater is contaminated with harmful viruses increases, and water purification is recommended.

In areas where human waste is present, a popular wild camping spot near a stream, for instance, water needs both filtration and purification. There, the concerns are ‘dirty’ water (particles, bacteria, and protozoa) and viruses.

What are the different outdoor water filters and water purifiers capable of?

The next part is a bit technical, but hopefully, it will shed some light on the capabilities of the 5 main water treatment methods: filtering, UV-light, chemical treatment, heat, and ultrafiltration. What do they remove? And under which circumstances do they work?

 Large particlesProtozoa Bacteria VirusesMulticellular parasites Heavy metals
Microfilter yesyesyesnoyesonly with active carbon
UltraViolet lightnoyesyesyesno no
Chemical treatment (tablets/ drops)nonot all of themyesyesno no
Heat (Boiling)noyesyesyesyes no
Ultra filtration (0.02)yesyesyesyesyesonly with active carbon

Water filters

Most water filters these days have a hollow fiber membrane water filter. Hundreds of small straws are bundled together to create a filter. A water filter needs a pore size with a minimum of 2 microns to remove bacteria and protozoa. If the pore size is bigger, bacteria can slip through. Water filters are effective in both clear and highly turbid water. Water filters, however, do not protect against viruses.  

Water purifiers

Water purification methods such as UV light, water purification tablets or simply boiling the water all inactivate bacteria, protozoa, and viruses. But these water purification methods all have one thing in common. It doesn’t remove anything from the water. If the water has brown color or contains silt it will still be brown and contains the silt after purification. When looking in more detail into what water purifiers are capable of, you will see some flaws. They do not always protect against all protozoa and parasites. 

Water purification: chemical treatment

Water purification tablets or drops have been used for decades. They do not always provide 100% protection against all protozoa (cryptosporidium) or larger parasites (worms). Water purification tablets are less effective in cloudy water. For backcountry use, it is recommended to use ‘clear’ water or pre-filter the water before using them. Most tablets require a waiting period, usually 30 minutes but up to 4 hours.

Water purification: UV light

Ultraviolet light treatments are effective against bacteria, protozoa, and viruses. And unlike most chemicals, they don’t give a particular taste to the water.  

UV light treatment may sound high-tech, but it is only effective in clear water. If the water is silty, muddy, or discolored, particles in the water can shield the microbes from the light’s effects. Also, multicellular parasites (worms) can survive the UV light treatment. For backcountry use, it is recommended to find a ‘clear’ water source or pre-filter the water before using UV light.

As you can see both tablets, drops, or UV light all work better when it’s combined with a filter, in particular in the outdoor when water can be cloudy. 

Water purification: Boiling

Boiling is one of the most effective ways to purify water. It kills all pathogens and requires simply the heating of water for one minute or 3 minutes above 2000 m. Even when water is murky or cloudy.

Water purification: Ultrafiltration

Ultra-filtration is the only ‘stand-alone system’  to remove particulates, protozoa, bacteria, worms ánd viruses. Ultra-filtration works the same as a water filter. With a 100 times smaller pore size of 0.02 micron, it also blocks the passage of viruses. Although the name would suggest we are talking about water filtration, ultra-filtration falls under the category ‘water purifier’, because it also protects against viruses. Sounds perfect right? The downside of ultrafiltration systems is that they are filtering to such a small pore size, that they tend to clog quickly. They have a relatively short life span, making it less ideal for longer periods of travel.

Remove heavy metals from water

Water can also be contaminated with heavy metals (copper, lead, arsenic, mercury, etc). But note that most water filters and water purifiers do NOT remove heavy metals. The focus of water filters and water purifiers is to remove microorganisms that could cause immediate harm. Heavy metals are generally only harmful after repeated and long-term exposure.

If you still want to reduce the level of heavy metals in your drinking water you could opt for a water filter that contains activated carbon. Activated carbon adsorbs heavy metals and other chemicals (pesticides, VOC).

Which water treatment should I use in which situation?

Based on the countries you are traveling, to and the main water source you get your water from, you might be interested in only a water filter,  only a water purifier, or a combination of both. A few examples. 

Situation 1: Get water from a mountain stream in Norway

  • Use a water filter. You want to remove possible particles, bacteria, and protozoa. Harmful viruses are of less concern, the next village is 40 kilometers downstream.

Situation 2: Fill my water bottles from a water tap in a city in Colombia

  • Use a water purifier (tablets, drops, UV SteriPen) or boil the water before drinking it. The water from the tap looks clear, so there is no need to remove particles. But the overall sanitation infrastructure is not well developed. You want to eliminate possible bacteria, parasites, and viruses.

Situation 3: Get water from a stream close to a mining village in Peru.

  • Use a combination of a water filter and a water purifier. First, use the water filter to remove the sediment. This also removes possible protozoa and bacteria. Next, use a water purifier to kill possible viruses.
  • The water is possibly contaminated with heavy metals from the mines. It is recommended to not use water in the vicinity of the mine. However, because you are only passing through the region with short potential exposure to heavy metal contaminants, you shouldn’t be too worried about it. Sadly, the people that live there and drink contaminated water day in and day out for a long period of time are the ones at risk to get serious health effects.

Examples of outdoor water filters and water purifiers

Water filters and water purifiers come in many sizes and forms. As it is an essential piece of equipment for outdoor life, we always opt for proven quality. These brands stand out. MSR and Sawyer. Here are three examples of high-quality outdoor water filters and water purifiers resp.:

Outdoor water filters

  • MSR Autoflow Gravity Filter 2 and 4 liters
    Very convenient to filter large amounts of water. You fill the ‘dirty water bag’, attach the hose with the filter element, and attach an Ortlieb clean water bag at the end of the hose. Within 15 minutes you have filtered up to four liters. The best thing is, you can leave it and it does the work for you. In the meantime, you pitch the tent or make a cup of coffee. It is a little bit heavier and bulkier than the other filters.
  • MSR trailshot micro filter
    Very convenient as it is small and lightweight. You do need a lot of squeezing to filter several liters. But it is fantastic if you’re underway and want to filter small amounts of water.
  • Sawyer squeeze mini filter
    The one almost everyone knows and uses. Fill up the plastic bag, attach the filter and squeeze the bag. It’s quicker than the MSR trail shot. The plastic bag does tend to wear down relatively quickly. But replacements can be bought. You can also use it for your camel bag. Attach the hoses on each end and voila. 

Outdoor water purifiers

  • Tablets
    You can find these in almost any pharmacy and are the most used water purifiers. 
  • Aquamira Drops
    A tiny drop of chlorine dioxide in your water bottle does the trick. The water will taste the same, so no chlorine taste. On top of that, unlike many other water purification drops, it is effective against any virus, protozoa, and bacteria.
  • Steripen UV Adventurer Opti
    It uses UV filter as a purifying method. It is an electrical device run on battery. It is small and lightweight so it is easy to take with you on any outdoor trip.


    As a halogen, chlorine is a highly efficient disinfectant, and is added to public water supplies to kill disease-causing pathogens, such as bacteria, viruses, and protozoans, that commonly grow in water supply reservoirs, on the walls of water mains and in storage tanks. The microscopic agents of many diseases such as cholera, typhoid fever, and dysentery killed countless people annually before disinfection methods were employed routinely

  2. Thanks for sharing! I’ve been using WaterDrop for years, with my husband, kids, and a dog. The capacity is enough for our daily water supply. The device is exquisitely designed.

Leave a Reply

Your email address will not be published.