Choosing the best way to treat your backcountry water can be tough. From pump filters to UV light, the market is full of options, and navigating today’s advanced technologies can be intimidating. But each treatment method has its pros and cons depending on the type of water you expect to encounter. In this two-part series, we’re helping you understand how each method works and what it’s designed to do—so you can make the decision that’s right for you and the water you might find.
Today: pumps, gravity-fed filters, and the category of small, personal devices like bottles, squeeze, and drink-thru filters. In part two: UV light, chemicals, combination treatments and boiling.
Microfilters vs. Purifiers
First, it’s important to know the difference between a microfilter and a purifier. Microfilters are typically designed to remove protozoan parasites (like cryptosporidium and giardia), as well as bacteria. Microfilters are generally considered sufficient for backcountry travelers in U.S. and Canadian wildernesses. A purifier, by definition, removes the threat of bacteria, protozoa and viruses. International travelers and those stocking emergency kits should seek out a purifier, as the risk of viral infection is greater in areas where human waste can contaminate water sources.
How Devices Remove Threats: What’s Happening Inside?
Next, you can think of the treatment devices in this article as two parts: the filter element inside that cleans the water; and the part of the device that controls how the water is forced through that filter element (the device’s “form factor”).
The technologies that make up the filter element are called filter media and vary from device to device. Some are more reliable than others in certain conditions. Here’s a look at the most common types of filter media and how they clean your water:
Hollow fiber technology: Think of a bundle of tiny straws, each full of microscopic pores. Their walls allow water to flow through, but block the harmful pathogens and dirt. Because the fibers physically remove the contaminants, hollow fiber technology is very reliable for treating many real-world water conditions. Hollow fibers offer very high flow rates, but some can be damaged by drops or freezing temps.
Ceramic: Typically a cylinder with a maze of microscopic holes that also physically block the contaminants. Ceramic cartridges don’t offer as much surface area, resulting in a slower flow rate. But even heavy clogging can be quickly reversed with a little scrubbing.
Activated Carbon: A block or granulated core. Carbon works by adsorption, attracting contaminants to its surface where they get stuck. Carbon is great for removing secondary contaminates like tastes and odors. But it can lose effectiveness when flow rates or contamination levels are high. Therefore, MSR does not rely on it for removing the immediate threats.
Silica Depth: An old term for a ceramic filter.
Other Adsorptive Media: If a device doesn’t use one of the above, it likely uses some technology that relies on adsorption. Like carbon, adsportive media are good for reducing tastes and odors from clear water. But they are not reliable for most backcountry water. If water contains particles like sediment, these filters can become overwhelmed quickly, allowing threats through. More, they don’t indicate when they’re “full,” so you never know whether your filter is still doing its job.
Comparing Your Treatment Device Options
Now that you know how the water is cleaned, let’s look at your options for moving it through the filter—these are the forms you’ll see on the shelf.
Pump Microfilters/Purifiers
The pump is one of the most common and highly trusted forms. A hand pump forces water through the filter element. The element is oftentimes ceramic, hollow fiber, glass fibers, or cellulose. Some also have a layer of carbon to remove tastes and odors.
Their durability, reliability and ease of use have made them the mainstay of backcountry travelers for decades. They often remove sediment as well as the pathogens, making them ideal for situations when you’re not sure what kind of water—clear, turbid, silty—you’ll find.
Most pumps have flow rates around 1 liter per minute. The majority are compact and about 16 oz. or less. A great one will feature a cartridge that can treat over 1,000 liters. Each MSR pump can be cleaned in the field and those with hollow fiber cartridges offer an in-field integrity test.
The downside to pumps? You must remain by the water source and do the pumping yourself. Traditionally, they’re best suited for solo travelers and pairs.
Gravity Filters
Gravity filters are fast, easy and practically do all the work for you. They’re so effortless that many people are instant converts. Their filter mechanism is similar to a pump, but here, gravity forces the water through. You do have to find a tree branch or other way to elevate the dirty reservoir so that gravity can pull the water down. Reliable filters often use hollow fiber or glass fiber, but other media exist.
Like pumps, gravity filters are great for wilderness travelers. They’re ideal for groups and basecamps because they often hold up to several liters. Most are pretty fast, but their real advantage lies in filtering your water all while you set up camp or prep meals.
Gravity filters roll up compact and often weigh less than a pump. In general, their cartridges don’t last quite as long, but using the clearest water possible helps increase their longevity. Most can be cleaned to maintain high flow rates. Those that use hollow fiber can be damaged by freezing or drops, so it’s good to look for one that offers an in-field integrity test, like the MSR AutoFlow microfilter.
Bottle / Squeeze / Drink-Thru Filters
The main advantage of this class of small, personal filters is low cost and complexity—the drinking bottle, collection bag, or straw, and its filter element are contained in one unit. These devices are meant for fast and light performance and/or ultimate convenience. They offer limited capacity and flow rates, so they’re best suited for individuals on day activities, like hiking, running or mountain biking, or as back-up filters.
Many of the options available use adsorptive media (carbon, coconut shell carbon, etc.), so they are not a reliable way to remove the harmful microorganisms; though some do use hollow or glass fiber.
The squeeze and drink-thru filters can be ultralight. The bottles are about a half pound or less. Although the convenience factor is very high, these devices can sometimes sacrifice practical functionality:
- Water collection can be awkward, such as lying in the dirt to reach the water source.
- You may have to carry around the dirty collection bag.
- You may not be able to fill up other containers with the water you treat.
- They generally don’t offer integrity tests.
- Often they’re single-person devices, so everyone in the group must carry their own.
So how do you choose the best option for you?
Do your homework. First, understand which technology the device uses to clean your water. Because some do not reliably remove pathogens, it’s important to evaluate the technology if you’re headed into the backcountry or anywhere microorganisms are a concern. Then, it’s really just up to you to decide which form factor best suits your needs, preferences and types of adventures.