How to Choose a Water Filter

Grayl water filter

When participating in any kind of outdoor recreation, we require a minimum of two liters of water a day to stay healthy. In other words: at least 68 ounces, half a gallon, 2 Nalgene bottles, or 3 standard Hydro Flasks (to put it in layman’s terms for our fellow “Bendites”). The key to drinking this amount of water safely (to avoid major gastrointestinal issues, a.k.a. a really bad time) without having to carry the full weight with you is to choose a good water treatment system.

Our March collection is all about hydration, and, as many of you outdoorsy folk may know, water purification and filtration play a big part in this when you’re in the backcountry. There are many new and varied choices out there, and while we can only introduce our subscribers to a small number of curated products each month, we want to make sure you’re prepared to enjoy your outdoor excursions to the fullest this Spring. Behold, our handy round-up of treatment methods to help you narrow it down.

Water filters vs water purifiers: There’s a difference!

Water treatment options generally work to minimize debris floating around in the water and to eliminate the “Big Three” — protozoa, bacteria, and viruses. As such, the key difference between a water filter and a water purifier is the size of the microorganism each combats.

Water filters work by physically straining out protozoan cysts (such as Cryptosporidium and Giardia lamblia) and bacteria (such as E. coli, Salmonella, Campylobacter, and Shigella). These are concerns if you’re traveling in the U.S. and Canada.

Water purifiers combat protozoa, bacteria, and viruses (such as hepatitis A, rotavirus, and norovirus), which are too small for most filters to effectively catch. This is ideal if you’re traveling in less-developed areas of the world.

Pump Filters and Purifiers

These cylinders have a built-in element that lets you slurp (insert sound effects here) water directly from the source. They’re also human-powered, meaning no batteries or fuel consumption required. The Grayl from our Winter Obsidian collection works with just one “press,” giving you filtered and purified water in less than 15 seconds!


  • You can process the exact amount of water you need.
  • Water can be pulled from shallow sources.
  • Water is quickly drinkable.


  • Pumping can be a chore, especially at the end of a long day of backpacking.
  • Field cleaning of the element is required.
  • Weight and bulk are greater than other treatment methods.
  • Limited use to one person.
  • The number of moving parts can increase the likelihood of equipment failure.

Bottom line: Pumps are popular, but the number of moving parts can result in equipment failure, putting you in quite the predicament if this is your only treatment method available.

Gravity Filters and Purifiers

“Set it and forget it”: just fill the reservoir, find a suitable place to hang it up, and wait. While this requires minimal effort, it’s important to keep track of which bag is the “dirty” (untreated) one and which is clean to avoid the exact uncomfortable situation the system was designed to remedy.


  • Gravity does the work for you.
  • You can easily process large quantities of water for a big group.
  • The element or cartridge is replaceable.


  • The treatment process is slower than pumping.
  • Shallow water sources can make it challenging to fill a reservoir.
  • Field cleaning of the element is required.
  • Must keep track of ‘clean’ and ‘dirty’ containers.

Bottom line: This is the simplest, best option for large groups--as long as you have a big enough water source and somewhere to hang it, and don’t mind waiting.

Bottles with filtering straws or lids

These bottles come with a built-in filter that is either a part of the lid or incorporated as a straw. The user fills up the bottle with water, which passes through a filter as it’s consumed.


  • Treatment is easy and water is quickly drinkable.
  • Element or cartridge is replaceable.
  • On average, lighter and cost less than pump and gravity filters.


  • Water quantity is limited by bottle size.
  • Field cleaning of the element is required.

Bottom line: As long as water sources will be readily available during your trek, this is a fast, painless option. That said, you only get one bottle at a time, making it unsuitable for groups.

Chemicals Drops or Tablets

Products are typically iodine- or chlorine-based and are effective against protozoa, bacteria, and viruses. Simply add them to gathered water and wait. The Purinize drops in our March collection naturally disinfect and clarify water from any freshwater source without chemical disinfectants (and make it taste good, too).


  • Easy to use.
  • Inexpensive, small, and light.
  • An excellent backup method to pack in case your main filter breaks.


  • Wait time before drinking is 30 min - 4 hrs.
  • Iodine products have a chemical taste (can be countered by taste-neutralizer tablets).
  • Iodine products can be a concern to pregnant women.
  • Not reusable--once you’re out, you’re out.

Bottom line: Reliable, simple solution if you don’t mind the wait or the taste. Great for ultralight backpackers. Many people like having tablets as a backup system (and they’re always a good idea to include in an emergency kit).

Ultraviolet (UV) Light Purifiers

All these pen-style devices require you to do is push a button, stir, and stop when its UV light turns off (after about 60 seconds) Voila! You have treated water inside a bottle.


  • Treatment is easy and water is quickly drinkable.
  • No element cleaning or replacement are ever needed.


  • Requires batteries.
  • Silty or cloudy water impairs effectiveness.
  • Multiple treatments are required to produce large quantities.

Bottom line: These are highly effective and popular with international travelers and the ultralight crowd, but you’ll likely need to prefilter and carry some chemical tablets as back up.


You can always boil water to purify it. Bring water to a rolling boil for 1 minute; if you’re above 6,500 feet, boil it for 3 minutes.


  • The only additional supply you need to pack along is extra fuel.
  • Murky water doesn’t impair effectiveness.
  • Serves as a readily available backup method in case your main filter breaks.


  • Time and effort required to bring water to a boil (and cool after).
  • If this is your primary treatment method, you need to pack an extra fuel container.
  • Problematic at elevation, where boiling cold or frozen water requires extra time and fuel.

Bottom line: May not be practical on the go, but, despite its drawbacks, this age-old solution is an effective treatment system to combat the full spectrum of biological pathogens.

Important things to remember

Taking a few key precautions will make any treatment method more effective.

  • Separate and clearly designate dirty and clean water containers.
  • Read the directions and take time to familiarize yourself with your treatment system before you take it out into the wild.
  • Regularly clean your system to ensure longevity and increase effectiveness.
  • Seek out clean water, as sediment impairs effectiveness. If only murky sources are available, use a prefilter.
  • Keep your hands clean with hand sanitizer.
  • It never hurts to have a backup plan.
  • Keep camp, toilet and dishwashing areas at least 200 feet from any water source. Learn more about LNT principles here.


As more and more of us explore wild places, contamination levels will rise. Even if the water looks pristine, it may be teeming with microscopic foes. Having a good water treatment plan is crucial to a successful trip. Once you have that on lock, you’ll be ready to get out there!

What’s your preferred water filtration or purification system? Tell us in the comments!