When it comes to water purification tablets in the backcountry, there can be no messing around.
Failing to properly disinfect water, even seemingly “pure” water, can result in serious illness or even death.
That’s why I was completely dismayed when I read through the reviews of water purification tablets on the internet. Many contained false information and almost all of them lacked a clear understand of what the real dangers are in the backcountry.
I immediately started doing my own research on the types of pathogens you encounter and the different treatments that are effective against each of them.
Having a Ph.D. in environmental chemistry and published my own science on contaminants in water, I was able to sort through the good and bad information that is out there.
I wrote these water purification tablet reviews to share the correct information on purifying water in the backcountry. Be sure to check out the infographic below to get the quick, most important info.
Table of Contents:
- Different Kinds of Water Purification Tablets
- Things that Water Purification Tablets Will NOT Remove
- Water Purification Tablet Reviews
- Guide to Safe Water Purification Tablet Use
- Conclusion
Different Kinds of Water Purification Tablets
Water purification tablets typically use one of three agents for disinfection: Iodine, chlorine dioxide, or other forms of chlorine. I am putting all forms of chlorine other than chlorine dioxide into one category because they all work in the same way.
Each type of water purification tablet has its own strengths and weaknesses and we will review these below.
Iodine
Iodine water purification tablets are effective at killing viruses, bacteria, and some protozoa like giardia but not effective against cryptosporidium. The downside of iodine is that it leaves a chemical smell and taste. This can be neutralized with vitamin C or ascorbic acid tablets. Also, pregnant women or anyone with a thyroid condition should not use iodine tablets.
Another downside to iodine water purification tablets is that the active chemical can break down when exposed to light. This is the reason they usually come in a dark jar. But you should still try to store them in a dark place and check the expiration date before you intend to use them.
Chlorine Dioxide
Chlorine dioxide is effective against viruses, bacteria and giardia in 30 minutes and effective against cryptosporidium in 4 hours. It is not unlike bleach in its chemical composition but actually behaves very differently.
Chlorine dioxide does leave an unpleasant taste but not nearly as strong as iodine tablets. The taste, however, can’t be neutralized with vitamin C as Iodine tablets can.
The major benefit of chlorine dioxide is that it is the only type of water purification tablet that kills cryptosporidium, or crypto. Another great benefit is that it is very soluble in cold water, making it a great choice if you’re purifying frigid waters.
Free Chlorine
The term “chlorine” is misused a lot in water purification information and it can be a source of major confusion. Chlorine is an atom that combines with other atoms to make molecules.
There are millions of different molecules that contain chlorine atoms so it doesn’t make sense to say water is treated with chlorine; it should be specified which form of chlorine is being used.
When talking about chlorine in terms of water disinfection, chlorine is usually meant to mean hypochlorite: either sodium or calcium hypochlorite, which is household bleach.
However, there are many different chemicals that contain chlorine atoms that are used to treat water. A common one used in water purification tablets is sodium dichloroisocyanurate. This is not the same thing as bleach but works on pathogens in the same way.
Water purification tablets that use sodium dichloroisocyanurate sometimes claim that their tablets don’t contain chlorine. What they mean is that the tablets don’t contain bleach but they absolutely do contain chlorine atoms.
I even read on one webpage “Our chlorine dioxide tablets don’t contain chlorine!” This is an oxymoron or, at the very least, imprecise. What they mean by this claim is that chlorine dioxide doesn’t produce free chlorine atoms in the same way bleach does (see the section below on how water purification tablets work).
Things that Water Purification Tablets Will NOT Remove
Tablets can break some chemicals down but don’t remove all chemical pollution. Furthermore, sometimes the break-down products of the chemicals are more toxic than the original chemical!
Fortunately, chemical pollution is typically not a major concern when hiking and backpacking, depending on where you are. You should be suspicious when hiking within 20 miles of any chemical manufacturing facility. Chemicals from these facilities are known to travel through the air and pollute waters downwind (which could be upstream).
If you suspect your waters are polluted with chemicals, the best course of action is to find better water. The second best course of action is to use a carbon-based filter. These filters are effective at removing a wide variety of chemicals.
Tablets also don’t remove suspended sediments as a filter does. Actually, if your water is overly murky (lots of suspended sediments) this can make water purification tablets less effective.
If sediment is present in your water, you should let it settle for at least two hours before carefully pouring the water into a new bottle (decanting), leaving the settled sediment behind.
Water Purification Tablet Reviews
1. Top Choice: Katadyn Micropur MP1
Active Ingredient: Chlroine Dioxide
Effective Against: Viruses, Bacteria, Protozoa
Katadyn Micropur MP1 water purification tablets are well-priced and give a mild taste to the water, which is better than what most tablets give to water. The tablets are individually packaged which is convenient compared to one large bottle. One tablet treats one quart so they’re simple to use.
These tablets are my top choice because they use chlorine dioxide which treats all three types of pathogens, they decently priced, and the company is trustworthy.
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2. Potable Aqua with PA+Plus
Active Ingredient: Iodine
Effective against: viruses, bacteria, some protozoa (including giardia)
Ineffective against: Cryptosporidium
Potable Aqua recognized that people don’t like the taste of iodine so their solution was to include a second tablet that neutralizes the taste. The second tablet is the “PA+” and is simply ascorbic acid (Vitamin C). This reacts with the residual iodine leftover after it has done its job of killing the pathogens in the water.
The result is much better tasting water than when treated with iodine or chlorine dioxide alone. It might not taste quite like fresh spring water but at least you know it’s free from giardia.
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3. Aquatabs
Active ingredient: Free Chlorine (in the form of sodium dichloroisocyanurate)
Effective against: viruses, bacteria, some protozoa (including giardia)
Ineffective against: Cryptosporidium
Aquatabs is a major manufacturer of disinfectant water purification tablets. The marketing is mainly aimed at water purification in developing countries, disaster relief, and military use. But their tablets are absolutely useful for backcountry water purification as well.
Millions of Aquatabs tablets are used every year so they are definitely a major company in water purification worldwide.
A chlorine compound is the active ingredient, meaning they are effective against viruses, bacteria, and giardia but not cryptosporidium.
A quick note on the apparently various brands of Aquatabs: there is actually only one brand of Aquatabs. Several other companies have sold Aquatabs in their own cases or in a “kit” and put their own brand on the kit but they use the same tablets (Aquatabs). This has led to many review sites (sites that don’t do their homework) giving various brands that sell Aquatabs different reviews as if they are different water purification tablets, which they are not.
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4. Potable Aqua Chlorine Dioxide Water Purification Tablets
Active Ingredient: Chlorine Dioxide
Effective against: viruses, bacteria, and protozoa
Potable aqua makes two kinds of tablets: iodine and chlorine dioxide. The iodine tablets (#2 on this list) come with a second tablet that enhances taste but that only works with iodine. It won’t work with the chlorine dioxide tablets so you’re kind of stuck with the chlorine dioxide taste. Fortunately, it’s not nearly as strong as the iodine aftertaste.
Also fortunate is the fact that chlorine dioxide kills cryptosporidium which iodine does not. That means these tablets treat all three kinds of pathogens found in backcountry waters.
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5. Aquamira Water Purifier Tablets
Active Ingredient: Chlorine Dioxide
Effective against: viruses, bacteria, and protozoa
Aquamira brags that they are registered with the EPA for water purification which is a good thing, I guess. Nevertheless, the tablets work wonders on nasty waters. Probably the strongest of all tablets on this list, and likely the most effective.
The only reason these tablets didn’t get my top choice is that there is a fairly strong taste and smell. And it is even more noticeable before they are done working.
Even though all tablets require a full four hours to kill cryptosporidium, give these tabs a full four hours before drinking even if you’re not worried about crypto. Otherwise, the chemical smell is pretty bad.
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6. Ef Chlor Water Purification Tablets
Active Ingredient: Free Chlorine (in the form of sodium dichloroisocyanurate)
Effective against: viruses, bacteria, some protozoa (including giardia)
Ineffective against: cryptosporidium
Ef Chlor is similar to aquatabs in that they contain the same active ingredient, a chemical that contains chlorine and releases free chlorine for disinfection. Their marketing, as with Aquatabs, is geared more towards emergency situations and developing countries than it is towards backcountry water treatment. But they are still useful in the backcountry…just not against crypto.
They claim to be effective in slightly turbid (cloudy) water but the actual level of dissolved solids they claim to be effective against is pretty low: 5 ppm. If you have no choice but to use these tablets in cloudy water, you can double the dose.
Per tablet, Ef Chlor is cheap but you can only buy packs of 100. If you’re only keeping water purification tablets for emergencies or don’t use them often, these are probably not a good option.
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7. Lifesystems Chlorine Dioxide Tablets
Active Ingredient: Chlorine Dioxide
Effective against: viruses, bacteria, and protozoa
These tablets are very similar to other chlorine dioxide tablets like Aquamira and Potable Aqua in that they use the same active ingredient and are thus effective against the same pathogens.
Chlorine dioxide is the most effective type of water purification tablet and thus we like this type of tablet over others. The advantage this tablet has over other chlorine dioxide tablets is the tough carrying case it comes in.
The downside is that it’s only available in the UK.
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Guide to Safe Water Purification Tablet Use
Beyond just buying the right tablets, you need to know a little about the pathogens that make you sick, where these pathogens are found, and how to effectively use your tablets. This info could keep you from getting a water-borne infection one day!
Be sure to check out the infographic below for a quick and easy guide to safely and effectively using water purification tablets.
Things That Make You Sick (Pathogens)
Pathogens are any microorganism that can cause disease. There are three types of pathogens that make you sick when you drink contaminated water in the backcountry: viruses, bacteria, and protozoa.
Viruses
Viruses are the least common pathogen encountered by hikers and backpackers but they are still important. The viruses that are found in some waters are pretty nasty, so they should definitely be on your radar.
These include enterovirus, hepatitis A, norovirus, rotavirus, and many others.
Viruses are most often transmitted from human to human so water near a lot of human traffic (for example, downstream of a city or town) is more likely to contain viruses than very remote waters. Water in developing countries is also much more likely to contain viruses.
All three types of water purification tablets are effective at killing viruses in water.
Bacteria
Bacteria are single cell organisms that are present in all water, everywhere. Some are harmful, many are not. Harmful bacteria include Salmonella, E. coli, Campylobater, Shigella, and several more.
Harmful bacteria are found in higher amounts where animals are present like cattle or pack animals. Beaver dams also create ponds that become a cesspool of decaying matter that spawn bacteria.
Even the most remote waters contain harmful bacteria. One study found 12% of remote sites (sites rarely visited by humans) to contain the harmful bacteria coliform.
All three types of water purification tablets are effective at killing bacteria in water.
Protozoa
Protozoa are single-cell organisms that behave more like animals than bacteria. They can be parasites or not and can make you sick either way. They are definitely something you should be aware of in the backcountry.
Protozoa, like viruses, can be spread from person to person and even from pets to people. If you are with someone that is sick, or you have a pet that is sick, be extra careful to practice good hygiene such as washing your hands often to protect yourself. Protozoa most commonly spread through fecal matter.
The two main types of protozoa that contaminate backcountry water are giardia and cryptosporidium (also known as crypto for short).
The treatment of cryptosporidium in particular is where water purification tablets differ in effectiveness.
Cryptosporidium (Crypto)
Crypto is found all around the world, including every region of the US. However, the risk of crypto is higher in developing countries. It can live in chlorinated waters and salt water for days so don’t think swimming pools or the ocean are safe.
Iodine tablets and tablets that use free chlorine are not effective against crypto but chlorine dioxide is low to moderately effective.
Filters with a pore size of less than 1 micron are highly effective at removing crypto. The most effective way to remove cryptosporidium from water is a combination of sub-micron filtration and followed by treatment with chlorine dioxide.
Treatment of crypto with chlorine dioxide tablets takes four hours. So plan ahead if you intend to use this treatment.
Giardia (Giardia intestinalis)
Giardia is a protozoan parasite that is known to give heinous diarrhea. Infection from giardia is called giardiasis and is one of the most common waterborne diseases in the US.
Giardia is found in many lakes, ponds, creeks, and streams. It is not only found in stagnant water, although higher levels of it may be present in non-flowing pools contaminated with animal feces.
Giardia is sometimes called “beaver fever” because beaver ponds are notorious breeding grounds for both bacteria and protozoa, giardia being the most common of these.
Raw or undercooked food can be contaminated with giardia and make you sick when you eat it. Giardia can also be spread by people or pets that have it.
If you are around someone that may be sick with giardiasis, be careful to practice good hygiene to protect yourself.
When to Use Water Purification Tablets Over a Filter
There are two main reasons to use water purification tablets instead of a water filter: viruses and convenience.
Viruses
Backpacking water filters can remove protozoa and bacteria, which are the two most common things in backcountry water that will make you sick. But viruses are smaller than protozoa and bacteria so they can pass through the pores of water filters.
Water filters do not remove viruses but all types of water purification tablets kill them.
When do you need to worry about viruses in water?
The threat of viruses from water in the backcountry (where human traffic is low) of developed countries like the US and Canada is thought to be low. Viruses are a concern, however, in less developed countries or even in developed countries in areas with higher human traffic.
Humans transmit viruses so any water where humans are nearby potentially contains them and should be disinfected with water purification tablets.
Convenience
Water purification tablets are small, lightweight, and cheap, making them super convenient for many situations. When it’s not practical to carry a water filter, tablets are your best choice. You should keep some in your day pack for emergencies.
How Water Purification Tablets Work
Iodine and chlorine-based (except chlorine dioxide, see below) tablets work in a similar way. The molecules from the tablets are able to exchange an iodine or a chlorine atom for a hydrogen atom in the molecules from the pathogen. This causes these molecules to stop functioning or fall apart altogether, rendering the pathogen inactive.
Chlorine dioxide works slightly differently in that it gives an electron to the molecules of the pathogen instead of whole chlorine or iodine atom. This process is called oxidation and chlorine dioxide is called an oxidizer. The end result is the same, though: the molecules within the pathogen stop working or fall apart and the pathogen is no longer active.
Evaluating a Water Source for Drinking
Sometimes you have a choice of where to take water from, sometimes you don’t. Knowing the potential hazards of a water source can effect your decision on specific locations to take water from (for example, different points in a river) but also how to treat that water.
Here are some helpful questions that will help you evaluate a potential water source:
Is the water flowing?
The water doesn’t have to be constantly moving but it’s better if it is. At a minimum, the water should have an inlet and outlet. It’s best not to take standing water like puddles or troughs. Animals may come and drink from and contaminate them when they do. That contamination stays for a long time.
What is upstream of the water? Towns? Factories?
If there are potentially a lot of people upstream of the water source (for example, if your water source is a large river), you will need to treat for viruses as well as protozoa and bacteria. It may be a good idea to seek out a tributary that is cleaner.
Are there any chemical industries, incineration facilities, or other places that might put pollution into the air within 20 miles?
Facilities that put pollution into the air can pollute waters that are upstream or downstream. It’s best to not drink water if you know these locations are nearby. I recommend not drinking water within 20 miles of a known polluter, but this is just a rough guideline because the amount of pollution decreases with distance from the polluter. As a side note – unless the water is very heavily polluted with chemicals, these waters won’t make you sick as fast as bacteria, viruses, or protozoa. But even low levels of chemical pollution is not good for your long term health.
What elevation am I at?
In general, lower altitude waters have a higher risk of contamination. The main source is livestock, so if you’re in an area with known livestock grazing be sure to either find better water or treat it properly before drinking. Another threat is beaver ponds. Beaver ponds are a cesspool for bacteria and protozoa and one could be upstream of you. High altitude waters are usually above where animals graze and beaver ponds.
How cloudy is the water?
Lots of suspended sediments make water purification tablets less effective. It’s best to not take water from cascades or waterfalls. If your water is cloudy, let it settle until clear and then decant (pour the clear water off the top) the water into another bottle for treatment.
The Myth of Drinkable Springs
Almost every backpacker will swear that they have drunk out of a mountain spring and it was the best water they’ve ever had. Water coming directly from a spring has been filtered through miles of porous rock and comes out looking crystal clear and tasing amazing! But it may not be totally clean at the microscopic level.
Contrary to (very) popular opinion, even the clearest of mountain springs should be treated with water purification tablets. Over and over again, scientists have traced back giardia and viral infections to drinking mountain spring water. You can find a great collection of these studies here.
Conclusion
Not all water purification tablets are equal. The main difference is that tablets with chlorine dioxide kill cryptosporidium, so these tablets are recommended. If you’re not too worried about cryptosporidium, iodine and chlorine tablets work in a similar manner but the main difference is the taste. Iodine has a stronger taste but can be neutralized by a reaction with Vitamin C.
Knowing where to take water from and how best to treat it is crucial in the backcountry. You must take water purification seriously because infection from a water-borne pathogen in certain situations can be life-threatening.
If you’re interested in staying safe when you go hiking, you should read 9 Essential Survival Tips and Why Day Hikers Are Most At Risk.
Are you into bushcraft or do you want to be? Check out 31 Awesome Bushcraft Skills and How to Master Them.
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