How Do Portable Water Filters Work? - Moosejaw

Water Treatment Guide

There are microscopic bugs, viruses and gross stuff in the world. That's a fact. Even though you can't see them, they're out there, hanging around in natural water sources, waiting to make you sick. It's like a tiny, tiny horror movie in every sip of pond water. Luckily, there are some simple steps you can take to safeguard against these unseen menaces. Step 1: Purify your drinking water when backpacking. End of list. Some filters or treatments work better for certain hiking trips, so I've compiled some info to help you find the best water filter for you.

Check out these bugs and microns.
Gross, gross, and gross.

Bugs / Microns

Know your enemy

Call the Microscopic Exterminators

At some point in history, some smart people figured out that there are tiny harmful organisms living in water. It had to be a terrible discovery. If it were me who first figured it out, I'd been like, "Oh c'mon!" Then I would have done like a thousand spit-takes. Now that we know all about them, it's not such a big deal. Here is a brief description of the disgusting things that you want to keep out of your body.

Protozoa: Giardia and Cryptosporidium are the biggest enemies to those drinking unfiltered water in North America. These tiny parasites will wreak havoc on your intestines and can take up to two weeks for you to feel their effects. Fortunately, they're easy to conquer with a simple camp water filter. Chemical treatments like chlorine dioxide will work but are not ideal as they can take up to 4 hours before making your water safe for consumption.

Bacteria Bacteria are small organisms that can affect your body relatively quickly (within 6 hours) but are also easily treated with filters or purifiers.

Viruses are smaller than both protozoa and bacteria and are impossible to simply filter out. Viruses that affect humans can only reach water sources through human feces (yuck) so most of the developed world won't have to worry about them. If you're planning a trip to an area where it is a concern, you'll need a water purifier or chemical treatment to ensure that your drinking water is safe.

Water Filters Comparison

Check out what each type of water filter is effective against, how they rank for perforamnce, and some pros and cons of each.

Water Filters Comparison + Ratings

Here are some details about each type of water filtration option, what they are effective against, and how they rank in terms of speed, weight, and their ease of use.

  Protozoa Bacteria Viruses Speed Weight Ease of Use
Pump Filter X *
Gravity Filter X
Squeeze Filter X
UV Filter
Chemicals ✔ **
  * A few pump filters can handle filtering viruses

** Does NOT always kill cryptosporidium

Water Filters Pros + Cons

Check out the crucial pros and cons for each type of water filtration so you can find a filter that works for the type of hiking trips you usually take.

  Pros Cons
Pump Filter • Very fast
• Can filter from shallow water sources
• Not the lightest option
• More parts that could potentially fail
Gravity Filter • Set it up and relax
• Great for large groups
• Need to keep dirty and clean components separate
• Can be difficult to fill from shallow water sources
Squeeze Filter • Filter on the go
• Very light weight
• Not good for groups
UV Filter • Takes up very little pack space
• Futuristic and super light
• Often requires pre-filtering
• Uses batteries
Chemicals • Very light weight
• Very packable
• Can be used as an emergency backup
• Most chemicals make water taste bad, especially iodine
• Long wait until water is drinkable
• Prolonged use of iodine is not recommended
Boiling • Kills everything
• Good backup option
• Tedious
• Uses a lot of fuel

The MSR Guardian is the most advanced backcountry pump water purifier ever. That's what they keep telling us anyway.
The MSR Guardian is the most advanced backcountry pump water purifier ever. That's what they keep telling us anyway.
Gravity filters are great for a variety of trip lenghts. And lazy people.
Gravity filters are great for a variety of trip lenghts. And lazy people.
UV light purifiers are fun and cool, but you'll need extra batteries, just in case.
UV light purifiers are fun and cool, but you'll need extra batteries, just in case.

Water Purification

Don't tell me what I decan or decant do

Filtering vs Treating

There are two general methods of making your water drinkable. Just a heads up, "drinkable" is often referred to as "potable." Another heads up, "potable" is pronounced like pote-able. At least that's how I sound it out in my head. Anyway, the two methods are filtering or treating. I'll describe them right NOW!

Water filters purify water by passing it through, well.... filters, which block the bad things. They are typically made of either ceramic or fiberglass. The pores on these filters are small enough to let water molecules pass through, but block bacteria (like e coli) and protozoa (like giardia or cryptosporidium). Just for the sake of learning, giardia and cryptosporidium (often referred to as cysts) and certain bacteria require filter cartridge pore sizes of 0.2 microns or less to be completely removed. Some filters will also contain a carbon element, which improves the flavor of the water.

Pump Filters: Pump water filters use some of your energy to force water through the filter. Just plop the "dirty" hose into a water source, and get pumping. They are great for immediate results, as you can have a Nalgene full of safe drinking water in no time (well, depending on how fast you can pump). Plus they work great on the go, when you just need a bit of water to fill up a bottle before hitting the trail again. The drawback is that as the filter gets older, it takes more and more energy to pump. Look for a model that is cleanable, allowing you to get your output flow back to almost new.

Gravity Filters: Gravity filters use the same filters as pump filters, but allow gravity to do all the work for you, like a natural butler. Depending on the water source, it may be difficult to fill up the "dirty" water container, but once you have it going, you just relax at camp and let the water filter do the rest of the work. These systems are generally lighter than pump filters, and are the optimal choice in most situations. Around a camp site, it's often easier to grab a ton of dirty water, hang it on a tree, and let it continually supply you with water. This can cut out trips back to the water source, and occasional pumping sessions.

Squeeze Filters:: These function a lot like pump filters, but they don't require all the extra weight and housing material of the pumps. They usually involve squeezing a bottle or a pouch to force the water through a filter and into your water bottle or mouth. They're a quick solo option for a backpacking water filter.

Water treatments purify water by killing off the harmful unseen threats. Their big advantage is that they can handle viruses in addition to bacteria and protozoa. Viruses aren't the most common threat, but in certain parts of the world they definitely need to be addressed. You'll need to pre-filter your water to get out any debris. Straining it through a bandanna or shirt will do the job.

UV Light: Purifying your water with UV light is like something straight out of the future. Just activate the purifier device in your water after you filter like you're some sort of cyber-sorcerer waving around a wand. They run on batteries, so make sure you have enough power for your whole trip.

Chemicals: You can use chemical drops (often chlorine dioxide or iodine) or tablets to treat and purify your water outdoors. It's not nearly as dangerous as it sounds and you don't have to be a scientist. Once correctly applied to your water, this stuff straight up kills all the bad stuff. Massacre-style. Caution: some chemicals leave a bad taste. More caution: make sure you get the water left on the threads or lid of your bottle (do this by leaving the lid slightly loose and shaking it). A third caution: cryptosporidium is resistant to chemicals.

Your pump filter works as fast as you do.
Your pump filter works as fast as you do.
Gravity filters do the filtering work for you, but it's on you to collect the water.
Gravity filters do the filtering work for you, but it's on you to collect the water.

Filter Times + Ease of Use

Patience is a virtue. It's also an old-fashioned name, I think.

It's all about speed vs effort.

Some of your decision will be based on how long you're willing to wait for potable water and/or how hard you want to work for it. There is no perfect solution, and each purification method has its own benefits and drawbacks. Here's a quick little rundown of what to expect from each method.

Pump Filters - The power is yours. You can work that thing as fast as you want. A common output rate is one liter in slightly over a minute but this can change depending on how much sediment is in the water, how old the filter is and how many times you feel like pumping. If you would rather expend your energy hiking than a water filter you need to pump is not for you.

Gravity Filters - These also provide drinkable water in a short amount of time, similar to the rate of pump filters, but without the pumping action. However, you will need to collect water into a bag, and find a good spot to hang it (if you don't feel like holding it). While some call it the lazy-man’s outdoor water filter, I call it tasty-drinking without the work.

Squeeze Filters - The flow on these things is typically slower than pump or gravity filters, but it has the added convenience of being usable on the go without much hassle at all. It is useful for grabbing small amounts of water to keep you moving. A water filter more convenient for solo hiking and cramming into small spaces of your backpack.

UV Light - UV light can treat a liter of water in about 90 seconds. That's only 180 half-seconds. It is fairly simple to use, the main difficulty being that you have to pre-filter your water. If there is a lot of debris in the water source you're using, you'll want to screen that stuff out. A cloth or shirt will get the job done. Some of the UV lights even come with a pre-filter that attaches to a Nalgene. Plus you have to constantly move the light around in the water for the 90 seconds. It’s a portable water purifier that is handy on the trail and for travel.

Chemicals - Treating water with chemicals takes a little while. The exact time will vary depending on what chemicals you're using, so BE SURE TO READ THE DIRECTIONS. Sorry for yelling, but it's important. These times could be anywhere from 15 minutes to up to four hours, so be sure to allow yourself some time for the chemicals to do their thing before you drink. A good backup to have in the outdoors, just in case your other water filter goes down.

A good gravity filter is suitable for most trip lengths.
A good gravity filter is suitable for most trip lengths.

Trip Length

The longer the trip, the more clean water you'll need. Pretty simple.

"Stay hydrated please." - Your Body

Some backpacking water filters work better than others depending on the length of your trip. UV purifiers will work great for a weekend or so but to keep them going you'll have to carry extra batteries, which makes them less than ideal for any long to longish trips. Pumps are also great for short to mid-length trips, especially hikes where you'll make frequent, short stops throughout the day. Treatment drops or tablets are the lightest option and are perfect for long treks, just keep in mind their inability to treat cryptosporidium as efficiently as a filter. Gravity filters are a nice compromise on weight and convenience for longer trips, and since most are field cleanable, you won't have to worry about output slowing as your trip goes on.

Maintain your water filter frequently, you guys. That gross water will muck it up.
Maintain your water filter frequently, you guys. That gross water will muck it up.


Your filter cartridge literally becomes clogged with the bodies of slain adversaries. Pretty brutal.

Proper Care = Consistent Performance

After using your water filter for an extended amount of time, cleaning will be necessary when you return home from the hiking trip. Water containing silt or debris will exacerbate the issue, and you will notice a decrease in output. It's a good idea to clean them after each trip but if you forget, most models are easily disassembled and cleaned on the trail. For UV purifiers, the only upkeep you really need to worry about are batteries. Keep 'em fresh and you'll have no issues. Squeeze bottles are typically just replaced when the flow gets too low, which isn’t a big deal because they are generally less expensive and have a long life. For exact cleaning instructions, please refer to the directions that came with your filter.

Using your stove or an open fire to boil water is always a reliable option to purify it, but will take some time.

Boiling Water

I bet Celsius and Fahrenheit probably bullied Kelvin in high school.

Effective, but not efficient.

A less popular option for water treatment is the old standby: boiling. Remember, you'll need a rolling boil of at least one minute (up to three minutes at high elevations) to make sure you kill everything off. Just think about how hepatitis A is the most resilient thing you're killing off, then I'm sure you'll be patient with that boil. While boiling water gets rid of protozoa, bacteria and viruses, it's not usually the ideal solution. The amount of water you should be drinking in the backcountry would take an incredible amount of fuel to boil. More fuel = more weight and nobody wants that. Another disadvantage to boiling is waiting for your water to cool down, unless you like drinking scalding hot water. That being said, if you're cooking a meal near water which requires boiling water, you might as well just use untreated water. Remember again, one minute rolling boil. This will simply cut out the filtering step.

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