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Filtration for Trail Runners - FAQ with Athlete Hillary Allen

March 13, 2023
Filtration for Trail Runners - FAQ with Athlete Hillary Allen

For trail runners, the introduction of lightweight threaded filters has been a game changer for the way they run. Athletes are able to run farther into the backcountry with the confidence they will be able to find and drink potable water on the trail.

To better understand the importance of filtration while drinking from outdoor water sources, we took some time to sit down with HydraPak Athlete and professional Trail Runner Hillary Allen. Luckily for us, Hillary’s mom, Professor Glenda Taton-Allen is a microbiologist at Colorado State University and she provided us with some valuable information on the types of bacteria and parasites found in water and the types of filters needed to remove them.

Your mom, Glenda is a microbiologist, can she give us a brief overview on why filtration is important?

Of course! My mom has taught me a lot about the importance of filtration. I reached out to her for some info and this is what she shared:

“Filtration devices are a great way to stay confident that water is safe to drink. I think it also helps to have some working knowledge of what it is you are trying to filter out, and why you would want to choose a filter size that will keep you from getting sick.

Runner holding a flask filter Parasites and bacteria found in outdoor water sources are the most common cause of waterborne illnesses out on the trail. While E-Coli and Giardia are perhaps the most common cause of gastrointestinal distress, there are lots of other parasites and bacteria that can wreak havoc on the gut if ingested through contaminated water sources.
Most bacteria, including Escherichia coli, are in the size range of about 2 microns. Giardia cysts, the stage that is infective and very hearty in water because of a cyst wall that protects it, range from about 9-11 microns. Cryptosporidia oocysts, the infective stage for this protozoan parasite, has a thick wall that keeps it viable for long periods in the environment. It is very small, in the range of 4-5 microns. Entamoeba coli, another protozoan infective in the cyst stage, is about 10-35 microns; Entamoeba histolytica is a smaller cyst size ranging 10-20 microns. These are a few examples of the common parasites found in water. They are all transmitted by a fecal-oral route, generally through contaminated water.“
A millipore filter that is 2 microns is good for most filtering flasks. The problem is when you get much smaller than that, it takes much longer to filter unless you can apply some sort of pressure to increase the speed. With a super small millipore size of filter, you will also get a lot of particulate matter that will clog the filter.

Hillary, can you give us a quick rundown of how you stay hydrated when you are out trail running?

Hydration while running is very important, especially if you're running for many hours. I tend to drink to thirst, and when it's hot out, I generally aim to drink 500mL for every hour I'm out running. That can get really heavy for my 20 mile or 30 mile long runs in the mountains which can take anywhere from 4 hours to 8 hours!

When do you take a filter with you? How has it changed the way you plan your runs and adventures?

I take a filter with me on every long run I go on. Even on my local trails where I don't want to carry 5 liters of water at a time - I just check the map for water sources and bring my filter with me for refills. It has changed the way I'm able to train. I can go farther and be more self-sufficient, knowing that I'll have safe water to drink while I'm out. It's also allowed me to do big loops - say a 3 day running loop - as lightweight as possible. I can run to my camp spot without having to bring water with me - I can filter water at camp to make dinner and filter water again for the next day's adventure.

What is your preferred way to filter water on trail runs? What kind of water sources do you seek out?

Most of the time I'm filtering mountain streams in the backcountry of Colorado - if I'm in the mining country of Colorado, I still have to be careful of the sources due to run-off from mines and heavy metals. In a pinch I will also filter from stagnant ponds - this is something I had to do on a recent bike packing and running trip in New Mexico, where my only water source was a well that ranchers were also using for their life-stock.

You mentioned that you always race with a filter, can you touch on that?

During my long ultra marathon races most of the time there are plenty of aid stations where I can fill up with water and food, but in some of the races I've done, aid stations can be up to 50km apart - which can take up to 8 hours between aid. That's a very heavy pack if I'm carrying all my water with me - so what I do is to take my filter with me, so I can drink from water sources along

filtering in Europe

the way without having to worry about getting sick. Plus, having a filter with me when it's hot outside is a good way to have extra water to drink along the way.

You have raced all over the world, but you have spent the most time running in the US and Europe, can you talk about the different in filtration between the two?

In Europe there seem to be more potable water sources along the way, due to the number of refuges and farm houses in the back country. I can drink safely from those sources without worry, but in the US, things are far more remote and less developed in the backcountry, so I tend to drink from more 'wild' water sources in the US with more caution.

What tips do you have for trail runners looking to try using filters for the first time?

Don't let them dry out and be sure to rinse them after you use them since river water (or pond water) can have particulates that can clog the filter, and if they aren't cleaned, it can lead to your filter slowing down or not lasting as long! Also, I would get two filters!

You can learn more about Hillary and her trail and bike adventures on her website.