With so many water filtering and purifying methods on the the market, it's no wonder backpackers are searching for guides to sort through all the options. Choosing the best system can be a little overwhelming.
First, it’s worth a quick review of the microscopic critters hiding in your wilderness drinking water. Three types of beasties — bacteria (e.g. E. coli), protozoan cysts (e.g. Giardia and Cryptosporidium), and viruses (e.g. hepatitis A) — can be found in water sources around the world, and you don’t want to ingest any of them.
Depending on where you’re trekking, you might simply need to FILTER your water. Hikers in the United States, Canada, and other well-developed countries generally need a filtering system that catches or destroys bacteria and cysts. Viruses, like hepatitis A, aren’t a wilderness concern here in the United States, but world travelers trekking in Nepal or other less-developed countries need to PURIFY their water. Purifying will neutralize viruses as well as bacteria and protozoan cysts.
As you explore the options, you might find the filter or purifier you select for a personal trip isn’t the best option for a Girl Scout trip with 12 thirsty participants. Here are several filtering systems to consider. While not an exhaustive list, each certainly has a lot of merit.
Katadyn Hiker Microfilter, $79.95 Weight: 11 ounces
Dimensions: 6.5" x 3" x 2.4" Neutralizes: Bacteria and Protozoan Cysts
Old school and tried & true, the Katadyn pump filter remains a workhorse for groups. It's an excellent option, especially for areas with shallow pools — think late-season water sources. Now more than ever, water flow often runs low, and the small pre-filter can get into small pools and under surface debris. The Katadyn is super durable, though mind the pump handle which can break if too much uneven pressure is placed on it. To justify the weight, consider this filter as community gear for a group. While one person is absorbing this weight, others in the group will have the fuel, the stove, the cookpot, etc.
Platypus GravityWorks Water System, 4.0 Liter, $119.95 Weight: 11.5 ounces Dimensions: Filter 2" x 8.5" / Reservoir 17.7" x 9.1" Neutralizes: Bacteria and Protozoan Cysts
While pumping water might build character, gravity systems are laughably easy and well-suited for any size group. Simply fill the "dirty" bag with water, connect the hoses and filter cartridge, and watch the water pour into your Nalgene bottle while you relax in the shade. My hack — buy a universal QuickConnect Kit by Osprey and attach it to the Platypus output hose. Connect your group's water reservoirs directly to the output hose, and by time you’ve set up camp, everyone is watered up. (I leave the clean bag at home, reducing the weight of the overall system to 8 ounces.) I like the Platy for personal use just as much group use, but I especially appreciate the ability to effectively back flush the cartridge in the field. The cartridges can easily last through several seasons of backpacking trips, and the flow rate is fantastic.
Katadyn BeFree Water Filter Bottle, 1.0 Liter, $49.95 Weight: 2.3 ounces Dimensions: 11.3" x 3.5" x 2.8" Neutralizes: Bacteria and Protozoan Cysts
The BeFree became my go-to filter during COVID-19 when I down-sized all my gear to essentially "go solo" with our groups of Girl Scouts. The BeFree filter cartridge weighs 1.25 ounces, and it connects to any number of different sized bags. You can buy the 1-liter BeFree or even a 3-liter gravity system. I purchase just the cartridges and attach one directly to a 2-liter Hydrapak so I can quickly fill my water reservoir and also have a bag of extra water in camp. I like having a small, super lightweight personal system that filters quickly with terrific flow. A couple caveats here. One, the poor water quality (silt, algae, and pollen) will clog up the BeFree, and there’s no back flushing option. You can rinse or swish the filter with clean water and improve the flow, and with clear water, this filter will last me through several trips. Two, Katadyn lists the BeFree as able to filter 264 gallons. Depending on the size of your group, that might not be enough. Since the system is so lightweight, I don’t feel bad carrying an extra 1.5 ounce cartridge as a back-up.
Sawyer Squeeze Water Filter System, $38.95 Weight: 3 ounces Dimensions: Filter 5" x 2" / Pouch: 11" x 6" Neutralizes: Bacteria and Protozoan Cysts
Smart water bottles with Sawyer Squeeze filter cartridges (2.5 ounces) are ubiquitous among Pacific Crest Trail thru-hikers, which lends the system a certain amount of credibility for those looking for a personal and lightweight system. I’ve only used the Sawyer Mini, and I cannot recommend it. The Sawyer Squeeze (not the Mini), however, gets gold star reviews. It has a lifetime guarantee to filter unlimited gallons of water. (Back flushing maintains the filter in the field and between seasons.) Hacks galore exist to improve the lightweight Sawyer Squeeze experience. Attach the Sawyer Squeeze to a more durable bag (CNOC Vecto 2L, for example) and create a gravity system. Improve airflow into your Smart Water bottle by drilling side holes in the cap. Leave your back-flushing syringe at home by using the Smart Bottle mouth tip instead. Set aside a month of evenings to watch all the YouTube videos to find your perfect hack for this solo system, but start with this science wonk video from GearTest Outdoors for an excellent overview.
Katadyn Steripen Classic 3 UV Water Purifier with Prefilter, $99.95 Weight: 6.3 ounces (includes batteries) Dimensions: 7.3" x 1.7" x 1.7" Neutralizes: Bacteria, Protozoan Cysts, and Viruses
The only virus neutralizer on the list, this lightweight system purifies your water with UV light; I’ve used it around the world with excellent results. I especially like that the Steri-Pen is effortless. All those years of sitting on wet banks and doggedly pumping water has given me an appreciation for "less work is more fun." You simply press the button and stir your water until the UV light goes out. You do need to use the Steri-Pen correctly to ensure purification; water should be pre-filtered into a hard-sided bottle (not a soft reservoir), and you need to patiently follow the light indicators until the UV is finished. Advice from the school of hard knocks: pack an extra battery OF THE CORRECT SIZE in your emergency kit. (The Steripen is also available as a rechargeable unit.) And don’t drop it; the bulb is made of glass.
Regardless of the water system you choose, remind your Girl Scouts that all filters perform best — and last longest — when using the clearest possible water. With drier conditions on the trail these days, sometimes we must work a little harder and pre-filter our water, or walk a little farther to find a clear source, but it's worth the extra effort to extend the life of each filter.
Valerie is the founder of CAGS Backpackers and a Lead Backpacking Trainer for Girl Scouts San Diego. She has backpacked for over 40 years and spent the last 20 years guiding Girl Scouts on wilderness trips.