Filtering Your Water on the Appalachian Trail

As with all subjects regarding hiking on the AT, there is no absolute one way to do something.  Nothing is solely right or wrong.  What matters most is that it is right for you.  Here are my tips and suggestions for how to safely filter your water while hiking on the Appalachian Trail (or anywhere else).

Hopefully you have only heard stories about Giardia, and never actually experienced it, so to lower your chances of contracting this parasite on the trail, it’s important to filter the water you drink while hiking along the Appalachian Trail.  When I googled a definition of Giardia, I actually saw the words ‘explosive diarrhea’ in the description, so my thoughts are that it’s pretty bad.  It can be found in both food and water, and yes, you can get it from touching a doorknob or sharing a toilette with someone who has it.  It can spread through a hostel full of hikers, so don’t be afraid to ask if there’s been an outbreak or if anyone is sick when you stay at one.  Wash those hands!!!  Use your hand sanitizer often when sharing quarters with others.  Not everyone who drinks unfiltered water on the AT gets sick, but it can happen, and if you are dehydrated enough, death can happen.  It is treatable and can last from 3 days to a couple weeks.

But maybe you aren’t overly concerned about your chances of involuntarily crapping yourself for a few days and just want to know how does one take long hikes in the woods and not have to carry gallons of fresh water?  This I can help you with!

There are a number of excellent ways to filter water you find along the trail.

When you come to your water source, take notice of the surroundings.  Is the water sitting still, or is it moving?  Is the movement slow or is it swift?  Is it colored, muddy, or clear?  Is it running over rocks or algae?  Can you see if it is coming from the ground or a pipe?

IF THE WATER IS STAGNANT (let’s knock this one out first)

If you can, keep moving to another water source where the water is moving, but if you are in dire need and this is your only option, you could do these things to lessen the risk of getting sick (and worse) from contaminated water.

Filter, fire, treat – Hopefully you have access to perform all three, but in absolute emergency situations, at least make sure you can do one.
Use a bandana or your shirt as a first filter to remove dirt, and things we can’t see.
Run your water through your regular filtration system if you have one (always have one!)
Boil the water for 5 minutes.  This intense heat inactivates viruses and spores that can harm you.
Treat the water with iodine pills.  REI sells Potable Aqua Iodine Tablets for around $8.
*** Iodine tablets are best used for treating stagnant water.  Filtration systems are best used for moving water***  Always make sure to carry both.

If the water is severely stagnant and nasty, and you can, use all three methods.  Treat the water last!!  If you treat it first, you will filter out the treatment you just gave it.  If you don’t have any sort of treatment methods and no way to boil water, you can also burn rocks to a very high temperature and drop them in your water to heat the water to intense degrees.  You should only do this with small amounts of water at a time.

Make sure you carry a backup water filtering source.  This is the best way to ensure you can safely drink water in all circumstances.  You can die from the effects of drinking bad water, and the extra ounces it costs to your total pack weight is worth the insurance. My recommended water filtration systems are at the end of this.


Hooray!  Always a good first assessment!  More times than not, your filtration system is adequate enough to filter out any harmful bacteria.  I believe they filter out 99.99% of what we shouldn’t drink in moving clear water, and that’s a pretty good promise for a water filtration company to make.  Yea, they are safe.

  1. Check to see how deep the water is.  It’s best not to stir up the sediment from the bottom as it will quickly clog a filtration system and slow down the amount of water that is filtered per minute.  Trust me, when you are used to water flowing right out at 2 liters per 2 minutes, it gets annoying when it trickles down to 1/2 liter per 5 minutes.
  2. Look for water passing over rocks and light algae.  It is typically better to get water that moves over rocks and very light algae, but I have been reading about a recent scare with toxic algae blooms, so research what you can before setting out.
  3. Look upstream.  Is there something dead or really nasty right above where you are taking water from?  Is your dog laying in the water up stream?
    Quick moving water does not = safer water, so don’t risk not filtering your water because you found some rapidly moving water.
  4. PUH-LEASE DO NOT USE THE STREAMS TO PEE, WASH YOURSELF, YOUR HAIR, OR YOUR CLOTHES IN.  Take your water 200 feet AWAY from the water source and wash yourselves.  Do you want to get water that someone else upstream is washing in?  If you pay anything in your hiking career forward, keep the water clean.  I read once where some hikers came up on someone washing his underwear directly in the stream…  It looks inviting, but just NO.  Remember, everything you do out there has an impact.


Water filters  make it impossible for harmful bacteria (like salmonella or leptospirosis), protozoa, or cysts like E. coli, Giardia, Vibrio cholerae, and Salmonella typhi to pass through the filter.

1eb450a7-f7d4-4883-b59c-ecb011b86d9d[1]Sawyer mini filter:

This used to be my main and sole filtration system, but I now use it as my backup.  It is small and easy to store and is good for 100,000 gallons of water.  That’s a lot!  It weighs 2 oz.  I like it because I can screw it directly on to my water bottle and drink straight from the filter.

It only fits water bottles with screw tops like what you buy from a store, so it’s perfect if you start off with a couple liters of store bought water like Aquafina or Smart Water and then when you refill them, screw the Sawyer filter right to it.  For safety, I’d keep it in my pocket (in a ziploc) when not in use so it doesn’t get whacked by something or dirty. Don’t keep it stored in the Ziploc though, when it’s still wet or mold will happen.  DO NOT LET IT FREEZE OR GET EXPOSED TO FREEZING WEATHER or the filter will not work.  This is something I keep in my sleeping bag during cold temps.

It comes with a squeeze bag so you can load the water in the bag and filter it through that if you don’t want to carry a water bottle with you.  It’s cool, but then I discovered the next filtration system that works faster!!

Pros:  light, easy to use, good for staying on the go.  Comes with back flush device if it clogs.
Cons:  the flow isn’t great so you’ve got to really squeeze or suck to get a pampered amount of water out at a time.

Platypus  gravity filtration system:9a136226-43ae-4f42-9f66-8d34292b14b9[1]

I love this thing! Basically you put the unfiltered water in the bladder provided and attach the filter and hose, and the water moves through the system into whatever object you are storing your good water in, in a matter of minutes.  It’s wonderful for when you get to camp and fill your bladder up and hang it (or hold it) and let the water filter through to another bladder or your water bottle, while you do other things.  Basically it moves more water quickly and efficiently so you can do the other things you want to.  Plus the water tastes really good coming from this thing.  Don’t add water with a lot of sediment though, as it clogs easily and puts a big damper on the ‘quick filter’ process.

You can filter it directly from the dirty water bladder to a clean water bladder that you keep stored in your backpack.

Pros:  Super time efficient, light, has own storage case, fast filtering
Cons:  Clogs easily and doesn’t have a flushing device.  (you can google how to manually back flush it, but for the price, I feel it should come with one.) Takes up space.

Aqua Mira drops:

My new equipment BFF!!  This has officially replaced my Platypus as being my primary filtrating system…  I really hate saying that because  I love my Platypus so so much, and may carry it with me for old times sake for a while until I need to cut down on a few ounces of pack weight or space.

For the way I carry and filter my water (I carry two 1L water bottles on outside of pack and keep 2L in a bladder on reserve – or just carry four 1L bottles on my pack), this works really well for me.  How it works is, for a liter of water, you add 7 drops of one bottle into 7 drops of the other (they give you a little cap to put the mix in) and wait 5 min (or maybe it’s 3, I don’t have the instructions in front of me) Then you add that mix to your 1L bottle and shake it and let it work for 15 minutes, then it is ready to drink!  And the water tastes great!  Plus this also protects against viruses, whereas the filters mentioned only protect against bacteria.  Unlike iodine chemical treatment, chlorine dioxide is not harmful to ingest regularly.

If you compare the time it takes to filter water from the three mentioned above, whether you are waiting for a slow pouring filter, or a fast filter that you have to put together and hang and probably undo your pack to get to, or this one, the time is probably pretty similar between the 3.  The sawyer mini is perfect if you want to keep moving, because you can just screw it directly onto your store bought water bottle and squeeze or tilt it back into  your mouth, it just doesn’t pour at a rate that one enjoys when they are thirsty and really want to get some water down their throat.  (that being said, I have not tried Sawyer’s squeeze filter, so it probably is an improvement from the regular mini Sawyer)

Pros:  3oz weight includes both bottles and the cap.  Very effective and protects against viruses.  Very simple to manage and use.  Seriously, when you are too exhausted to lift one more finger, this method is a reward.
Cons:  If waiting 15 min to treat your water is a con then this is the only one I can think of, but like I mentioned earlier, when it comes down to treating the water, all methods take time in one form or another.  I also noticed a tangy taste to the water, but it might be user error.


Never leave home without them.  No matter how many filtration systems you take with you because you can’t decide which one you like the best, always make sure you have your iodine pills for stagnant water.  Remember, filters are for moving water, iodine pills are for non moving water yucky water.  Filters are for bacteria, pills are for viruses.  IODINE PILLS ARE FOR EMERGENCY USE.

Pros:  What you need for emergency use only
Cons:  Takes 30 minutes.  Not for regular or long term use.

I took this from a gear review site (Outdoor Gear Lab):  According to Potable Aqua, “Potable Aqua is intended only for the emergency disinfection of water and should not be used in any other way.” Iodine should not be ingested continuously over extended periods of time…”

I hope this information helps you as you plan your next big hiking adventure.  I remember thinking there was no way I could carry enough water for 3 or 4 days while hiking the first time on the AT.  Then I found out it’s not necessary.  I know many who just carry 2L of water at all times and fill up often, but I am too slow to get to the next water source with only 2 liters of water, so I carry 4.  It’s heavy but I feel safer knowing I have reserves.  While these systems are exactly what I use on my trips, please do your own research on the products to ensure they are right for you and your needs.

You should not risk being out there without a filtering system and a backup.

I hope you will subscribe to my blog and / or feel free to leave comments or questions.


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