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Clean drinking water is an absolute necessity. It's often said humans can survive three days without water, but during strenuous physical activity, this could be a generous estimate. However, rehydrating isn't as simple as drinking directly from the first pond or stream you find. Even if untreated water looks crystal clear, it may be packed with millions of pathogens that are invisible to the human eye.

In a cruel twist of fate, drinking the wrong water can do more harm than drinking nothing at all.

Waterfall and stream

To avoid becoming ill, you'll need to find a way to remove or inactivate these unseen microbes — which isn't always easy if you're fleeing a catastrophe. In the past, this meant setting up camp, building a fire, and boiling water — a laborious and time-consuming process. Today, there's a better way to provide clean water on the go. Portable water filter or purifier devices come in many shapes, sizes, and configurations, but they all share one key advantage: they can produce clean drinking water quickly and reliably, without the need to set up camp.

Waterborne Pathogens

To better understand water purity, you should be aware of the waterborne vectors that pose the biggest health threat: viruses, bacteria, and protozoan cysts — we'll call them the “Big Three.” Drinking water contaminated with any member of the Big Three family can cause diarrhea, vomiting, fever, fatigue, sudden weight loss, and even death. The most common examples of each are:

  • Bacteria: cholera, E. coli, salmonella
  • Protozoan cysts: amoebae, cryptosporidium, giardia
  • Viruses: hepatitis A, norovirus, rotavirus


Beyond the Big Three, you may also want to watch for chemicals (such as chlorine and pesticides) and heavy metals (like lead and arsenic). Unless these other contaminants are found in extremely high concentrations, such as in industrial runoff, they probably won't make you sick immediately. However, they can have long-term negative effects on your health.

Particulates, taste, and odor should also be considered. Although they may not be directly harmful to your health, nobody wants to drink murky, gritty, foul-smelling water. Ideally, filters and purifiers should also address these components.

Our Review Procedure

Unlike buyer's guides found in our competitors' pages or websites, RECOIL OFFGRID actually reviews the products. Thoroughly. We don't regurgitate manufacturers' ad copy, but instead test every item and provide our honest assessments. With that said, you'd practically need a PhD in microbiology to understand the dozens of standards and protocols governing water purity.


Adequately testing the purity of water to these exacting standards is impossible without sophisticated lab equipment and highly trained personnel. Off-the-shelf water test kits can't possibly detect the minuscule levels of contaminants we're dealing with here. Microbiological lab testing would be prohibitively expensive and time-consuming for the purposes of this guide. So, rather than focusing on verifying the accuracy of manufacturers' water purification claims, we have provided those claims at face value for comparative purposes.

We also evaluated the filter systems with a focus on practical concerns. These include ease of use, speed of filtration, the ability to clear murky water, and the ability to reduce unpleasant taste and odor.

We carried each device, and learned to use it correctly. Next, we sampled ordinary tap water with each purifier, to see if it altered the water's neutral taste in any way. Then, we simulated turbid or murky water by stirring in a set amount of fine particulate, and observed the clarity of the water produced by each filter. We then taste-tested the filtered water, estimating the system's ability to remove flavors and odors caused by pollutants.

Finally, we dismantled, cleaned, and reassembled each filter, and tested tap water again to establish if any residual taste remained from the turbid water test.

Comparing Effectiveness

Remember how we said we wouldn't get too technical? Well, bear with us, because we're going to need to bend that rule.

Water purifiers are typically measured and rated to remove 99.X percent of viruses, bacteria, or protozoan cysts. Each digit in this percentage represents a power of 10, also called a “log” (short for logarithm). For example, a filter rated to remove 99.99 percent of bacteria would be rated at a “4-log bacteria reduction.” If your water had exactly 1,000,000 microbes in it, a 4-log reduction would mean only 100 of those microbes would be left in the water after treatment — 999,900 microbes would be removed. A 6-log or 99.9999-percent reduction would leave only 1 microbe in the water.

LifeStraw Personal Water Filter in use 2

For the purposes of this comparison chart, the ● symbol represents one decimal place. So, ●●●● represents 99.9999 percent or 6-log reduction rate, ●●● represents 99.999 percent or 5-log, and so on.

According to NSF International and ANSI (two major safety certification organizations), the minimum standard for effective microbiological reduction is 99.9999 percent of bacteria (●●●●), 99.9 percent of protozoan cysts (●), and 99.99 percent of viruses (●●). This is based on a U.S. Environmental Protection Agency (EPA) report called the “Guide Standard and Protocol for Testing Microbiological Water Purifiers.”

Any purifier that meets or exceeds this standard, known as NSF/ANSI P231, can be said to effectively remove virtually all of these three contaminants present in water. Some purifiers actually exceed this NSF/ANSI standard, but as long as the rating is met for all three categories (bacteria, protozoa, and viruses), any difference in water purity beyond this standard can be considered negligible.

In simpler terms, more dots and checkmarks represent better performance.

BacteriaProtozoan CystsVirusesChemicalsHeavy MetalsParticulatesOdor & Taste
NSF/ANSI P231 Standard●●●●●●N/AN/AN/AN/A
Icon Lifesaver●●●●●●
Potable Aqua●●●●●●

Activated Carbon: What It Can & Can't Do

Activated carbon is found in several filters covered in this guide. This substance, also called activated charcoal, is highly porous and captures trace chemical elements found in water. This is especially useful for removing off-putting taste and odor, such as the chlorinated taste of tap water. It can also remove traces of other chemicals, heavy metals, and poisons (see “Poison Eraser” in Issue 15). As a result, filters or purifiers that address taste and odor typically incorporate an activated carbon component.


Activated charcoal can act as a “poison eraser” in the body, but it does not remove pathogens from water.

However — and this is an important point — an activated carbon filter shouldn't be seen as a water purifier by itself. Activated carbon doesn't treat or remove bacteria, protozoan cysts, or viruses. So, it can't prevent you from getting sick from these contaminants.

For comparison purposes, we reviewed a Brita Sport water bottle that exclusively uses an activated carbon filter. It may cost only $10, and it can make your water taste better, but it's not going to prevent the devastating health effects of a bacterial infection or waterborne parasite. Activated carbon filters like this Brita are fine for home use on clean tap water, but they certainly shouldn't be part of your emergency survival kit.

Water Filter & Purifier Buyer's Guide

H2O Hygiene - Filters & Purifiers

[products ids="7975, 7977, 7984, 7988, 7992, 7996, 8000, 8004, 8008"]

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