Water purification methods

November 8, 2023 10:43 AM

Initially thought of this in the context of a camping trip, but now also wondering about home safety purposes.

What's the latest on ensuring that water is drinkable/potable and won't kill you?

• Iodine, sure, but what are the limitations? How much water per tablet can it purify?

• Boiling? To what temperature, for how long? Which types of microbe is it effective against?

• I know next to nothing about filters/osmosis.

• As far as I know, basically all of the above are for bacteria only. Which is good and all, but what if the water has chemical toxins instead of just biological? (Unlikely for a camping trip, I know, but somewhat more plausible when it comes to, say, well-water for a house.) Is there anything that works then? How to even tell if this is the case?

posted by queen anne's remorse to Food & Drink (9 answers total)

Best answer: Iodine: Kills _most_ microbes / viruses. Follow the directions on the box for dosing and time / temperature. It generally does nothing for chemicals. I also recommend having some kool-aid or tang on hand to kill the aftertaste.

Boiling: Kills the microbes / viruses. CDC recommends 1 minute at a rolling boil. Bump that to 3 minutes if you are above 6,500ft (water boils at a lower temperature up here). Does nothing for chemicals.

Filtering: Removes the microbes. Some will also remove viruses (MSR Guardian, et. al.) If it also has a charcoal filter, it may also remove some chemicals.

For all of the above, you can use a coffee filter to remove most of the large particulates from the water before boiling / filtering / treating.

See also the CDC page at https://www.cdc.gov/healthywater/emergency/making-water-safe.html

For a camping trip, it depends on where you are. Viruses may be a factor if you are downstream from a population center or (in the case of a recent backpacking trip I was on) a large dead animal in the river upstream from where you are. Also, a lot of wilderness areas may have been the site of former mining operations (like the San Juans in Colorado). So you may also have some nasty chemicals leaching into the water system in random places. In those cases, get upstream of the old mining operation if you can. Otherwise, go far enough downstream that the contaminant is sufficiently diluted.

Personally, I now use an MSG Guardian when backpacking because I can filter enough to fill a 2L bladder in about 90 seconds and I don't need to deal with constantly cleaning it like my old filter. I have iodine tablets as a backup in case the filter breaks. My backpacking kit does double duty in the event that we have an issue with the water at home.
posted by SegFaultCoreDump at 11:02 AM on November 8, 2023 [4 favorites]

Best answer: I bought a small Sawyer brand filter for backpacking/camping (I think it's an older version of the Sawyer Squeeze?) but I actually use it more at home (I'm mostly a day hiker). My home tap water is safe to drink but I use the filter to e.g. purify water for my neti pot to make absolutely sure I don't get brain amoebas (obviously I can boil water in my home but I find the filter easier/more hands-off). My filter is a lot slower than SegFaultCoreDump's MSG Guardian.

I also carry iodine tabs when I'm backpacking/hiking in remote places but only as an emergency backup, I find them an unpleasant-tasting pain in the ass.
posted by mskyle at 11:29 AM on November 8, 2023

Best answer: I've got a Platypus ceramic filter that I use while camping that is good for bacteria but not viruses or chemicals. I've also got some purification tablets that are not iodine and are good against bacteria and viruses. Chemicals would be a worry but as I'm camping I figure that the water is fairly uncontaminated by them and I'm not going to be drinking all that much of it anyway. The last resort is just boiling water for a couple of minutes.
posted by any portmanteau in a storm at 12:05 PM on November 8, 2023

Best answer: For treating non-cloudy water and in emergency backup situations, I prefer a chlorine dioxide product such as Aquamira instead of iodine. It doesn't take any longer than iodine, it tastes a lot better, it's more effective against parasites, and there aren't health issues (it's the same method a lot of municipal water treatment plants use). However, if you're in an area where cryptosporidium is a concern you'll need to wait a LONG time for it to work, so you should bring a filter or purifier (or plan to boil) in such circumstances.

Here's a guide from the CDC [pdf] that compares different treatment methods.
posted by theory at 12:23 PM on November 8, 2023 [3 favorites]

Best answer: Sierra Club article
American Hiking Society article

Info in both articles aligns with what I've been told at Sierra Club backcountry training. Other methods mentioned in the article that aren't listed here yet: Bleach, UV pens.
posted by LionIndex at 12:24 PM on November 8, 2023

Best answer: If you’re curious about home filtration, you’d want to look into filters for private homeowner wells. I’m on town water so haven’t had to look into the details, but know plenty of people with wells. Some chemicals can’t really be filtered out - especially some of the nastier industrial, mining, or agricultural pollutants. There are various tests to detect them, but you’d use an alternate water source if that was an issue (i.e. bottled, or the US Army Corp has water tanker trailers that they can bring in and plop down in a town center in case of emergencies like the town water filtration plant getting flooded, or a train derailment spilling tons of some industrial chemical that gets into the local water supply). But lots of metals can be filtered out, using a combination of heavier duty filters (I don’t know the details) and salts (eg. water softeners)/other chemical filtration techniques (that I’m also not super clear on the details of). These sort of home well filtration systems tend to be larger (some I’ve seen are the size of those water bottles you get for office water filters), or have multiple components, or require adding the salts or other additives regularly; some need to be used regularly rather than sitting around dry (or at least, that was the case with something that some friends had installed at the bottom of their well, where it would deal with some metals before they had a chance to cause damage to other components of their water system, but their build schedule being delayed caused some potential issues of some sort); and all or most are generally much more expensive than a camping filter. So you wouldn’t really just have them on hand for the rare emergency - it would be much easier and cheaper to have some bottled water for emergencies instead.

There are also some larger scale filter systems that disaster relief agencies use, I gather, but I don’t know if they are just bigger versions of a really good camping filter, or if they are more nimble versions of home well filters?
posted by eviemath at 12:28 PM on November 8, 2023

Best answer: UV sterilisers were covered in the consumer crap-detector podcast Sliced Bread. tl;dr they are more marketing BS than the best thing since SB sliced bread.
posted by BobTheScientist at 12:44 PM on November 8, 2023

Best answer: Just a note to say that UV water purification methods are legit.

I have used all a Steripen UV device almost exclusively for the last decade’s worth of backpacking adventures (including 800ish miles on the Appalachian Trail and half of the John Muir trail…so far)…It’s fast, easy, effective against viruses, and on the handful of occasions where water is stagnant I’ve been able to pre-filter with a bandana. I don’t have to baby the filter (like the Sawyer squeeze)…just carry an extra set of batteries/make sure it’s charged before setting out.
posted by wearyaswater at 6:03 PM on November 8, 2023

Best answer: There are two kinds of filters - active (meaning you actively pump the water through the filter by squeezing, stepping on a foot pump, or pumping a hand pump) and passive (hang a bag up high, let gravity pull the water through the filter) For large amounts of water when you're not a in a rush, passive is much nicer. If you want a quick drink in the middle of a hike, then active might be nicer.
posted by mrgoldenbrown at 8:39 PM on November 8, 2023