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There are a few questions regarding safety of water purification, one regarding expiration date, another regarding iodine, but I know that there are more than one types of water purficiation tablets.

If I am using a water-pump filter. Is it necessary to combine this with a water purification tablet? Katadyn, a water filter company, suggests doing so.

However, this makes me question the safety of putting such chemicals into my drinking water. In general, is it best to just avoid it? Or are there any water purification tablets that are proven safe?

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    Note that Katadyn suggest to use tablets because they get rid of stuff which the filter doesn't. They are not suggesting to somehow first use tablets and then their filter to filter out the chemicals from the tablets...
    – fgysin
    Jan 8, 2020 at 13:55

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If I am using a water-pump filter. Is it necessary to combine this with a water purification tablet?

As discussed in this answer and at greater length here, the need to treat backcountry water before drinking it is largely a myth. Neither the filter nor the tablets are needed. You're better off focusing your efforts on avoiding the real reason that backpackers are likely to get sick, which is hand-to-mouth contamination. Practice good potty hygiene, and don't share pots with your hiking partners (whose gut flora your body hasn't got a tolerance for).

If you're traveling in the third world, or drinking water that you collected downstream from a poultry farm in Arkansas, that's a different matter. Filters work against protozoan cysts. Tablets kill bacteria and viruses. Another good option to consider is a steripen, which treats water using UV light. It kills cysts, bacteria, and viruses, is more compact than a filter, and is faster than tablets.

Katadyn, a water filter company, suggests doing so.

Katadyn sells tablets, so they have an economic interest in propagating myths about the need for water treatment.

However, this makes me question the safety of putting such chemicals into my drinking water. In general, is it best to just avoid it? Or are there any water purification tablets that are proven safe?

Iodine is a nutrient that your body needs. That's why they iodize salt. So the question is not really whether iodine is bad for you but whether a certain amount is good or bad for you. The lethal dose in humans is a couple of grams, and it kills you by oxidizing proteins. A typical concentration used for purifying drinking water is about 3 mg/liter, so by drinking a liter of water you're getting about a thousandth of the lethal dose. For comparison, a gram of iodized salt has about 0.02 mg of iodine.

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  • Unfortunately, third world countries are on the itinerary. So while I'm in those countries, should I always treat, then filter?
    – MarkE
    Aug 16, 2013 at 9:14
  • In that case, I think I would to make sure viruses are killed, and because the speed of medical response is probably lower.
    – Don Branson
    Aug 16, 2013 at 9:52
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    @MarkE: In your situation, I'd use a steripen. I've added some info about that to the answer.
    – user2169
    Aug 16, 2013 at 13:53
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    -1 for "Iodine is a nutrient that your body needs." Sodium is also an element your body needs. Try eating pure sodium sometime and let me know how that works out for you. (Disclaimer: That's a joke, don't actually eat it, you will die.) Also, the dose is crucially important: eat enough of any "essential nutrient" and you will also die. To evaluate the safety of iodine tablets, you have to consider their exact chemical composition and strength.
    – Nate Eldredge
    Aug 23, 2013 at 0:33
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    As someone who recently had Amoebic Dysentery from hiking in the Appalachians an getting bad water -- I'll always be treating/filtering/boiling. Even if I'd only get sick once every ten years... well you have to have it to get the point. It is pretty bad.
    – Russell Steen
    Sep 7, 2014 at 15:05
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Just as an addition:

For treatment and filter, I'd filter first, then treat. For 2 reasons:

  • After a while, filters get alive and things start growing.
  • Most of the chemical treatments work by oxidation. No use spending the oxidation capacity on stuff that can be oxidized, but could have been filtered out anyways.
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I currently use a Sawyer Filter without using purification. I carry iodine tablets as a backup. Iodine's been in use for decades, and I don't worry at all about using them when necessary. Ray J. recommends being smart about choosing your water sources, which I am. When I was a kid I drank straight from the streams without any purification or any problems, so perhaps I have some immunities from that. People today are way too worried about water purification, if you ask me. People in some countries survive worse water from their taps than we have from our streams. We also worry too much about chemicals, probably. Water is a chemical, and an extremely dangerous one in pure form.

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    Oh, the iodine tablets I use have some kind of citrus flavor to cut the flavor of the iodine, and the purified water tastes fine. It looks rusty, and I wouldn't drink it very day, but it's fine as a backup.
    – Don Branson
    Aug 16, 2013 at 1:21
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    "Water is a chemical, and an extremely dangerous one in pure form." What are you trying to say with this statement? In which sense is pure water dangerous?
    – Snijderfrey
    Jan 10, 2020 at 9:18
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The main concern about iodine tablets is exceeding the recommended daily dose of iodine your body can handle safely. In addition to that, iodine can not kill many of the protozoan cysts. The main concern about chlorine tablets is that they can not kill many of the protozoa. The main concern about the filters is the real size. Most of the viruses are smaller than to be filtered out. But almost all of the cysts and a great deal of bacteria can be filtered out. Boiling water is a good option, but many spores and cysts (like anthrax or Entamoeba hystolitica) can tolerate boiling water. Beside, heavy metals and many other chemical contaminants can not be removed by boiling water or using iodine or chlorine treatment.

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If you're worried about the safety of iodine or don't like the terrible taste, you could get some chlorine tablets. They cost about the same, but aren't as easy to find at general sports stores.

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  • And is chlorine safe then? If so it would be great if you could provide additional information (maybe scientific source).
    – Wills
    Sep 13, 2014 at 21:44

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