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Reviews > Water Treatment > Chemical Treatment > MSR MIOX Purifier > Owner Review by David McKinnon

September 14, 2011


NAME: David McKinnon
AGE: 41
LOCATION: Nashville TN U.S.
HEIGHT: 5' 9" (1.75 m)
WEIGHT: 170 lb (77.10 kg)

Backpacking Background: I've been backpacking fairly regularly for 25 years and try to average a 3 to 5 day trip 8 to 10 times a year. I typically hike Tennessee's state and national parks including the Smokies, but also try to make it to destinations such as the Rockies and Alaska when possible. I've been putting a greater emphasis on smarter gear choices and pack weight the past 4 to 5 years.


MSR MIOX Purifier

Manufacturer: Cascade Designs
Year of manufacture: 2007
Listed weight with batteries: 3.5 ounces (99 g)
Weight as delivered with batteries: 3.4 ounces (96 g)
Weight with salt in chamber and carry pouch: 4.1 ounces (116 g)
Variable weight: Extra salt and free-chlorine test strip quantities will vary with trip durations (10 test strips and test strip container weigh 0.5 ounces (14.2 g) plus 0.5 ounces (14.2 g) of salt cover most 3-5 day trips)
Length: 7 inches (18 cm)
Width: 1 inch (2.5 cm)
MSRP: US $139.99

Battery type: 2 x CR123
Battery life: Listed as 50+- gallons (200+- liters)

The MSR MIOX comes packaged with the MIOX treatment device (referred to as the MIOX "pen"), 1 ounce (28 g) of rock salt in a 3" (76 mm) square Ziploc-style bag, 2 CR123 Lithium batteries, 50 free-chlorine test strips in a 3" (76 mm) tall by 1 " (31.8 mm) diameter flip lid container. All items are stored in a 4 " (108 mm) by 8" (203 mm) pouch which has a mesh front, nylon back and locking draw string at the mouth opening.
Carry pouch, MIOX pen, test strip container, salt bag

Product Description:

The MSR MIOX purifier pen is a lightweight electronic water-treatment device that is designed to kill water-borne microorganisms. The device produces a mixed oxidant solution, hence the name MIOX. When this solution is added to potentially contaminated drinking water, it kills viruses, bacteria, Giardia, and Cryptosporidium.

The MIOX pen has 3 internal chambers: the battery chamber is located on the bottom of the unit and is accessed by a threaded cap. The salt and purifier cell chambers are on the top of the pen and are accessed by both a threaded cap on the very top of the unit, and a screw- off chamber below the top cap. The top salt cap and bottom battery cap are joined by a lanyard, which keeps either cap connected to the device if they are unscrewed individually. The salt and purifier cell chambers are separated by a 3/8" (9.5 mm) diameter screen that allows the salt to dissolve into the water as part of the treatment process.

MIOX pen

An activation button and indicator LED lights are stacked vertically down the shaft of the MIOX pen. A button click chart located near the bottom of the unit indicates the number of clicks required to treat certain amounts of water, but this measure can vary substantially as will be outlined further. The activation button is located about midway on the MIOX body. 3 indicator lights are located on the upper half of the device: a battery status LED, a salt status LED, and a RUN status LED that indicates the unit is in operation.

After salt and water are placed in their respective chambers, activation of the MIOX pen produces an electric current in the resulting salt-water mixture, which chemically creates the microorganism-killing mixed oxidant solution.

The in-a-nutshell operation instructions could read: put salt and water in their chambers, close lids, shake, open water chamber, click button and watch it fizz for a few seconds. When done fizzing, add the few drops of produced solution to the water supply. Test water if needed.

Battery chamber. Requires two CR123 batteries.

Purifier cell/water chamber. Electrical current is added to the salt water in this chamber to create the mixed oxidant solution.

Salt chamber. Uses any standard food grade rock salt.

Test strip and container with chart. The head of the test strip is dipped into the water for about one second. The resulting color when compared to the chart on the container indicates the relative water safety.

Field Information:

I have used the MSR MIOX for 4 years on approximately 36 hikes in a wide-ranging array of conditions and durations. Elevations have varied from about 300 feet (91 m) to 9000 feet (2743 m). Temperatures have ranged from 0 F (-18 C) to 95 F (35 C). Most trips ranged from 3-5 days. I have used the MIOX on clear sunny days, rainy days varying from light sprinkles to torrential downpours, and snowy days ranging from light snow to near white-out conditions.

Like all water treatment methods that I have used, the MIOX has its strengths and weaknesses but overall, I find it to be one of the better options on the market. Unlike water filters, the MIOX requires no pumping, virtually no cleaning, and does not have the potential to clog in the field. Perhaps my primary personal "like" of the MIOX is that, if operated correctly (proper amount of solution applied to appropriate amount of water), the MIOX adds little to none of the bitter flavor produced by many tablets and drops. The device also kills more potentially dangerous microorganisms than most other water treatment options. Unlike ultraviolet treatment methods, MIOX treatment is unaffected by the cloudiness of the water. A very important factor to me, MIOX -treated water can be tested with the provided free-chlorine strips to determine the effectiveness of the treatment. UV treatments can't be verified under questionable circumstances. A little verification adds a great deal of comfort with my drinking water when I'm miles into the backcountry.

There are, however, drawbacks to the MIOX. The multi-step process that produces the treatment solution comes with a learning curve. Salt and water are added to their respective chambers, sealed, and shaken to combine through the screen that separates them. If not enough of either ingredient is added, the combine can fail. Fortunately, the indicator LEDs warns of these types of issues. Once I get used to how much salt each treatment uses given a particular water source or water supply in a specific area, this is a non-issue. I highly recommend experimenting with the MIOX at length prior to taking it into the backcountry for the first time.

Perhaps my biggest issue with the MIOX pen is the inconsistent battery reading. On most trips of 40 F (4.4 C) temperatures or lower, the batteries must be warmed prior to use to avoid getting a "battery low" warning even on a fresh new set of the CR123s. Before using the MIOX in cold weather, I typically pop the batteries out and place them somewhere warm (pockets, hands etc) for about 30 minutes. MSR rates the battery life at 50+- gallons (200+- liters) but I've only gotten close to this quantity on new batteries in extremely warm conditions, so the safe bet is to keep a spare set on hand. Again, once I got used to this battery issue, it didn't affect my operation of the device.

Though the MIOX treatment means a certain death to most bad stuff living in water, the waiting time for this process can be a drawback. Most viruses and bacteria are killed within 15 minutes, Giardia in 30 minutes, but to ensure that Cryptosporidium is killed, the wait time is bumped up to 4 hours. If Crypto contamination is a possibility, proper water planning and rationing might be necessary with these wait times. Given the fact that some treatment methods don't kill Crypto, it is worth the wait to me if there is a possibility of this type of contamination. There have been a number of instances in which water sources were not what I expected and ended up drinking a batch treated with the MIOX a bit sooner than recommended, but I've never had a water related health issue in my four years of using the device.

A commonly raised concern with the MIOX is that, like tablets or drops, it does nothing to remove particulates (crunchies) from the water. On a trip to Denali, Alaska, we were dependant on glacier fed streams that were almost as much silt as they were water. I found that filtering the water with a bandana or coffee filter made this a non-issue. In my opinion, this certainly beats dealing with a repeatedly clogged filter.

I have found the click chart on the face of the MIOX to be a rough suggestion only as the number of actual clicks required vary surprisingly depending on water conditions. The chart indicates 1 click for liter of water, 2 clicks for 1 liter, 3 clicks for 2 liters and 4 clicks for 4 liters, with each subsequent click raising the potency of the produced solution. Once the solution is added to the drinking water, the free-chlorine test strips which are provided are dipped into the water and the depth of the resulting purple color on the strip indicates the relative treatment and safety of the water once the appropriate amount of time has passed. The number of clicks rarely corresponds to the amount of treatment actually needed to satisfy the test strip. If in doubt, I typically double the number of suggested clicks to be on the safe side and have never had an issue with water treated with the MIOX.

The MIOX is not the most glove or cold-hand friendly device. On a 5 day snowshoe trip in the Colorado Rockies I had several difficulties operating the unit in conditions where removing my gloves was not a very appealing idea. The small size and light-weight aspect of the MIOX dictate that the caps and activation button are also small. This renders them a bit awkward to use with heavy gloves. I learned to plan accordingly when temperatures were in the teens and single digits and to make sure I was out of the wind and as warm as possible to effectively operate the device after removing my gloves.


Like all water treatment techniques that I have used, there are advantages and disadvantages to the MIOX. I found that once I conquered the learning curve of a technique that really is unique in this application, the MIOX became my preferred treatment method. The MSR MIOX kills more microorganisms than many other techniques, was easy to use once I understood the nuances of the device, and has never failed me on hundreds of miles of backpacking.

Pros: Provides consistent and measurable water purification

If used in correct proportion, water tastes great

Lighter than filters and doesn't clog or require pumping

Cons: Does nothing for particulates in water

Cold weather functionality is a bit finicky

Requires a substantial initial learning curve

This report was created with the Report Writer Version 1. Copyright 2011. All rights reserved.

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Reviews > Water Treatment > Chemical Treatment > MSR MIOX Purifier > Owner Review by David McKinnon

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