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MSR Miox

rated 4.0 of 5 stars

The Miox has been discontinued. If you're looking for something new, check out the best water purifiers for 2024.

photo: MSR Miox water purifier

Still available used. Excellent, but for a very specific use. This device makes a chlorine dioxide mix that treats water about the same as chlorine dioxide tablets but it is always fresh. It's heavier than tablets but cheaper in the long run and for huge quantities. Its chlorine solution kills more than bleach does.


  • Cheaper than a case of tablets
  • Can treat huge quantities of water.
  • Kills viruses, bacteria, protozoa, and giardia well in a short time


  • Batteries run out
  • Device can (rarely) corrode and fail
  • Fiddly to use
  • Heavier than tablets
  • Does not remove dirt, crud, flavors
  • Only fair treatment of cryptosporidia cysts

The also discontinued MSR SE-200 (larger) and the still available H2gO and Potable Aqua Pure (similar to MIOX in size) do the same thing. They put electric current through concentrated salt water to separate the chlorine from the sodium in the salt and produce a fresh mix of active chlorine oxidants, like chorine dioxide tablets, stronger than regular bleach. You can treat huge amounts of water with these but MIOX can only make enough for 4 liters in a cycle.

Well made, needs to be emptied and cleaned to prevent corrosion.

Works great on viruses (which filters miss) and bacteria in 15 minutes, giardia and protozoa in 30 minutes, but it takes 4 hours to (mostly) treat cryptosporidia with chlorine dioxide, and drops don't remove crud, so I filter first if possible. 

This chlorine or chlorine dioxide method is one of the more effective methods of water treatment used in WHO and UN programs (look up WASH; water, sanitation and hygiene). The treated water can clean containers or food as well. 

Swimming pool test strips that show free chlorine up to 3.0 ppm (3 mg/liter) can replace the no-longer-available MSR strips. Search  Tests should show 2.0 at 30 min, 0.2 at 24h per CDC. WHO prefers at least 0.5 at time of drinking. 

The flavor of chlorine (which can be strong) can be removed with vitamin C or hydrogen peroxide but this inactivates the protective residual chlorine. Search for cdc dot gov preparing-international-travelers water-disinfection 


Lots of water treatment in many places worldwide x decades. Katadyn Pocket filter, MSR filters, Sawyers, Miox, tablets, etc.

Source: bought it used
Price Paid: $20

No nonsense use, however sadly discontinued.


  • The two ingredients needed, water and salt, will be always and everywhere available.


  • RTFM, you know how it works, otherwise leave it alone:-)

Living in Europe, Sweden is the place to be for me during holidays. Backpacking and traveling over water in my Canadian open canoe. Living from flyfishing and collecting edible plants, herbs, berries, plantroots and mushrooms. sometimes fresh roadkill or venison, if I was lucky, sometimes a squirrel or a hare. (don't ask me how;-) The water is commonly clear and clean, but one dead animal upstream will ruin your day for sure.

In the early days I used an MSR Miniworks, in combination with treatment drops, hard work, and expensive filters, nowadays a gravity filter and in case of doubt a few drops from the Miox. Paid €120 back then, but it still works fine, no corrosion on the elektrodes, but I'll use the tip of making brine, tthxx.

The treatment takes five minutes,  and I'll have enough safe water for the rest of the day. Every five days I produce some more to clean possibly grown biofilm in my water bottles and food containers. I hardly notice the chlorine smell, so I'm very happy.

By all means it lives up to my expectations. Bought six years ago a used Miox on amazon for $20 for a friend who became a backpacker in Sweden too. I'll try to find another one as a  spare in case of malfunction or loss the future. Mine is 18 years old if I'm correct. My MSR fuel burner is 40 years old, for which I had to make a new nozzle on my lathe because it is obsolete in the new red spare parts maintenancekit. I expect the same endurance from the miox:-)


Over 22 years of backpacking and canoeing in Sweden, Norway, and Finland, aprox 30-60 days a year, daily water from streams and lakes.

Source: bought it new
Price Paid: €120 new in outdorestore and €20 used at amazon

Upsides: It works and is lightweight, and kills some nasties that iodine tablets don't kill. When I'm hiking anywhere that there's good-tasting water available (e.g. the Sierra Nevada), this is what I take to handle purification duties. The chlorine taste is similar to many cities' water and is far less annoying than iodine taste. Consumables are cheap. There's no moving parts to break or wear out.

Downsides: It's not a filter, so doesn't improve the taste of the water (aside from removing tannins, that icky "dead leaf" taste, which however does use a lot of chlorine so overchlorinate) and doesn't remove floaties from the water. If you're hiking somewhere that the majority of water is scummy cow tank water, carry the extra pound of scrubbable ceramic-based filter with you (with a coffee filter prefilter), your taste buds will thank you.

A bit fussy with the residual chlorine strips (though you'll mostly use them for less-than-prestine water where you want to know how much to overchlorinate). Too expensive if you only go hiking a few times a year, you can get chlorine dioxide tablets that do the same thing. Does use batteries, and the batteries do need to be kept warm in cold weather for this thing to work right.

Price Paid: $99

The MSR Miox pen is a small compact water treatment unit. The original Miox Pen (identical in operation to the MSR commercial unit) was first issued to our soldiers in Afghanistan. It is lightweight and stores easily. It is also economical over time. I got many backpacking trips and water treatments out of a single salt tablet and the original set of batteries.

There is a big misconception among those who aren't familiar with the Miox and its chemical treatment engineering, and who rather simplistically dismiss the Miox Pen as only a 'chlorine maker'. The Miox Pen does NOT produce simple sodium hypochlorite (otherwise known as commercial bottled chlorine). Instead the unit uses salt, water and electrolysis to produce a complex compound of mixed oxidant chlorides that is effective against all bacteria, viruses and parasites, including crypto, which ordinary bottled commercial chlorine WILL NOT kill.

Another misconception is health effects. What some critics don't realize is that Miox has used the exact same technology to produce water treatment for third world and military applications for years with no ill effects. If it's safe enough for the U.N. and U.S. special forces, it's safe enough for me. I love my Miox!

Price Paid: $120

Purchased this unit for two uses. Primarily for traveling out of the USA and use on backpacking/camping trips where the water source will be relatively clear.

For traveling over the last two years I've taken along a Sweetwater filter and the MSR MIOX. The water sources have been not clear, little funky smelling and potential viral contaminate. Clear and clean tap water to drink. I found that by letting the water sit for a day the pool smell and flavor is reduced or disappears. For camping I still prefer the Sweetwater.

Positives are: Compact, relatively light, simple to use and effective against bacteria, protozoa and virus. A water purifier.

Negatives are: It's not a filter. So sediment, color, odor, chemical in your water can be a problem. The lithium A123 batteries do not last for a long trip (3-4L/day x 30days). Bring spares for an extended vacation.

4 Stars, not 5 because of its limitation of maybe having to drink unclear water and residual chlorine taste.

Price Paid: $79

Amazingly light, and extremely effective purification. I have used this for over 12 years and NEVER had an issue with it !


  • Simple
  • Very lightweight
  • NO tedious pumping required.
  • Amazingly effective purification


  • The photo batteries are somewhat expensive.

I have used this device for over 12 years; and in guiding groups of up to six people, I have NEVER had anyone suffer any stomach ailments or discomfort. Ever! But I do not use it the way the manual suggests. By using dirty murky water in the purification reservoir,  I found that friends' MIOX devices eventually corroded the electrodes and rendered them unusable.

Instead, what I do is carry a small 100 mL dropper bottle of sterile I.V. saline. It is this clean sterile saline solution that I drip into the purification reservoir,  which keeps the electrodes clean and effective. After every trip, I flush the reservoir with hot distilled water, and soak it for half an hour to completely dissolve and remove all traces of salt and impurities off the electrodes.

This unit has NEVER failed me, and I always carry two sets of spare batteries when I am out in the wilderness. An effective and bombproof product.


Extensive backpacking and kayaking in Western Canada, the Rocky Mountains, and the Pacific Northwest. Used to provide water for groups of six people for 4- or 5-day trips.

Source: bought it new
Price Paid: 150 Canadian dollars

I have owned and used the Miox for one ice climbing season and one summer backpacking season. While I would probably prefer a traditional water filter in the summer, in the dead of winter this isn't an option.

I find the Miox indispensible in the winter. The unit is small enough to store in your belay parka (to keep the batteries warm), easy to use with liner gloves, and the reactive chemicals work fast enough with warmed water (melted snow) to be drinkable within 15 minutes. In my opinion it's better than Aquamira unless you're an ultralight hiker counting the grams.

The unit is easy to use and the indicator lights make it virtually idiot-proof. Also, the option of double or triple dosing is a lot easier than using bottled chemicals. If you can get the water lukewarm, this little unit can do the rest. Use with a bandana "pre-filter" for great results.

Price Paid: $120 CDN

I picked this slick little unit up because I hate the taste of iodine and I didn't feel like hauling around a water filter. This unit is very small, light, and easy to use once you know how (figure it out at home first).

My complaint with the unit is that I was assuming I would be getting taste-free water treatment. This is not the case. It makes the water taste like rather heavily chlorinated city water, and smell faintly like a swimming pool. It's nowhere near as bad as iodine, but it was still an unfortunate and unexpected surprise. You could probably hide the taste with flavour crystals, but I like my water pure, especially in the outdoors.

Personally, I think I'll probably end up going with a standard water filter instead.

I picked up the MIOX unit before going on a Mt. Rainier climb. It's easy to use and as long as you follow the directions and wait times it will give you safe water (from virus, bacteria, etc.).

It does leave a slight taste and as my friend found out the solution it creates will act like bleach to your clothing if you spill it on yourself. The only issue I've found it that the test strips indicate a "too low" for the standard treatment. I solved this by treating for one step higher than the standard. It may just be the water sources I'm using. I don't consider a fault of the unit as it does its job.

Price Paid: $129

Excellent water purifier, small, light, compact, and reliable. It produces chlorine dioxide, the same effective chemical used in Aquamira and Micropur tabs, which means that it will kill crypto, unlike iodine or plain chlorine treatments.

I have found that the Miox Pen produces odorless, clean-tasting water with no chlorine taste, when properly used on backcountry water sources according to directions with proper dosages and wait times. Some people have poured the Miox Pen oxidants into already-chlorinated city water sources and decry the 'swimming pool' taste, not realizing that such a procedure will only intensify the taste of already-present residual chlorine. Read the directions and you should have no problems.

Price Paid: $110

I agree with some others: Yes, it does smell and taste like a swimming pool. MSR was not honest about that. I've used it hundreds of times over a year, in four continents. Besides the taste, the thing is amazing in every way. I tried to make as many travellers as possible feel bad about buying bottled water (it's a huge waste problem overseas) by showing them this thing.

Version reviewed: Military Version

Really like this unit. I use it as a backup and for purifying large amounts of water at a single time. I found that you must practice with this unit to get it right to avoid the "swimming pool" smell that most mention. It's small, highly portable, quick and efficient...what more can I say?

Price Paid: $96

Bought this for hiking and emergency situations. It will purify large amounts (liters) of water. Highly recommend practicing with this unit repeatedly until its use is 2nd nature. In an emergency situation, this will be time well spent. It's a great design, light and capable. Find some water and this thing will clean it up.

I purchased a Miox a few years ago. I am planning a week long trip on the river with my son, so I took the Miox out of storage and decided to test it before I took it to the river.

I'm glad I did because it doesn't work anymore. I have put new batteries and salt in it and it keeps giving me a low salt warning light. I guess it's back to the filter and the bleach.

Price Paid: $139

Although this seems wonderful product, it is of no use without any safety indicator strips. And if you live in the Netherlands it is impossible to find those in any shop (no reordering there), and if there is some found at the back of à shelf, it is grossly expired and does not work.

Ordering any by internet does not work also as all MSR products are not sent from US. So we are very disappointed with this product.

This is a cute little compact chlorine maker. If you want chlorinated water why not just bring a small bottle of bleach along? I'm returning mine because chlorine is bad for us.

Price Paid: $160 CA

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Price MSRP: $139.95
Historic Range: $27.95-$140.00
Reviewers Paid: $20.00-$139.00

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