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I'll be winter camping in a bare-bones cabin with 6 people for two nights and 4 people for a third night. By my estimate, we'll need a lot of water: 6gal 2nights + 4gal1night = 16gal. I plan to haul in a rigid 5gal of tap water to get us started, and there's a stream next to the cabin so water itself is not scarce. Since it'll be cold (mid-30's dF high, mid-20's dF low), I'm wary of using Sawyer filters as freezing damages them. That leaves me with boiling (a decent option as we'll be staying warm and cooking with a wood stove) and chemical treatment.

To reduce our boiling demands, I plan to bring a separate 5gal tote for our dish and hand washing purposes and use chemical treatment for that. I have this 5gal collapsible container and these Micropur MP1 water treatment tablets. Let's say I fill up the tote halfway at a time, approximately 2.5gal, that's about 10 liters. The tablets say 1 tablet per liter and wait four hours. My question is if that ratio changes as it scales up, and for water not directly consumed? As in, for 10 liters do I need all 10 tablets, or can I reduce that? I ask as I only have 20 to 40 of these tablets, though I could go pickup more. With over 5gal of water needs likely, these might not be the way to go.


A note about alternative chemical treatment: I have access to is 3% hydrogen peroxide. I read that 30mL of 3% hydrogen peroxide mixed with 1gal of water is sufficient. I have a 0.25gal bottle of hydrogen peroxide (946mL), which seems like enough to treat 30+gal of water with that ratio. If those treatment tablets are truly 1 per liter even when treating by the gallon, hydrogen peroxide seems like my best option, does that sound right to you?

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    Consider a reverse osmosis purifier. It works by pumping the water through a filter, using your muscle power. The purifier is roughly the size of a quart bottle, a bit larger. It is easy and quick to purify several quarts. BUT, the stream water we start with is in a remote area, and is clear, with the liklihood of upstream contamination low, and it has typically been oxygenated by small waterfalls, and turbulent flow. Personally, I would feel more comfortable using purification tabs or boiling in a frequented area with a gentle stream. (bp is lower the higher you go.) I may be irrational.
    – ab2
    Commented Feb 16 at 2:00
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    Where are you going? Depending on the place, you wouldn't even need treatment at all, and certainly not for cleaning. Mountain streams for instance are typically very clean.
    – PMF
    Commented Feb 16 at 14:44
  • A frequented state forest in the Northeast. Treatment is a standard expectation - most commonly boiling in winter here - but whether water used for cleaning needs the same amount (or any) treatment is really what I'm asking.
    – cr0
    Commented Feb 16 at 15:00
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    For my kid's school Outdoor Program, there was one trip that was cross-country skiing to yurts. The yurts had wood stoves for heat and water. We put a big pot on the stove and added snow as needed to keep water in the bottom and snow melting. There is no need to purify the result, assuming the snow is taken from an untouched snow bank.
    – Jon Custer
    Commented Feb 18 at 1:01

2 Answers 2

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Boiling is the most effective and cheapest method of cleaning up this much water. It does require some faffing about boiling volumes, letting them cool before putting in storage containers, then boiling more etc. However, it is highly effective against all the common pathogens. Filtration for these sorts of volumes is a lot of work too and you need the right sort of filter to get rid of viruses, which most people do not have access to and are very expensive.

I would use a portable cooker for this as it is very slow to boil on a fire unless the fire is designed as a cooker or has attachments for hanging water over the fire. Just be aware that if you are using a gas cooker, you need adequate air flow to prevent carbon monoxide production. An open window nearby or using near a chimney/flue should be sufficient. Just allow enough time for the water to cool afterwards - outside in a covered container should be fairly rapid at the temps mentioned in the question.

The CDS has a guide to creating safe water in an emergency. The information in there is a good guide on how to get safe water, which applies in your situation, even though it isn't an emergency. It even gives you some options which you didn't mention in your question.

The only really effective chemical method that most people have access to is the use of the chlorine tablets such as the M2 ones mentioned in the question. These contain chlorine dioxide, which is a fairly effective sterilizer for water. Bleach (usually sodium hypochlorite) is as effective as chlorine dioxide against bacteria and viruses, but less effective against protozoa.

I found an excellent book at the National Institutes for Health (NIH) titled Drinking Water and Health, volume 2. It is free to read and covers all the major chemicals used to treat water, including a section on chlorine dioxide, indicating that chlorine dioxide is effective against two of the major microorganisms that might cause you concern in drinking water - bacteria, viruses, but the data is lacking on protozoal cysts (such as Giardia and Cryptosporidium) and requires further study.

The CDC says that chlorine dioxide is highly effective against Giardia, but has low to moderate effectiveness against Cryptosporidium, and should be used in combination with filtration for effective removal of the protozoan.

Hydrogen peroxide is not at all effective for use in drinking water. To quote the book:

Although there has been some interest in using hydrogen peroxide as a disinfectant for wastewater (Taki and Hashimoto, 1977), it has been used more for control of bulking in the activated sludge waste treatment process (Sezgin et al., 1978). Its use in drinking water disinfection appears minimal.

Table II-20 in the book summarizes the data available, and shows that for common bacterial species, such as Escherichia coli, the inactivation after 300 minutes was less than 90% at a 3% concentration, so whoever told you that you could use 30 ml of 3% H2O2 per gallon was way way off. You certainly do NOT want to drink 3% hydrogen peroxide. 6% is used to bleach hair. If you have ingested small amounts of a 3% solution it is recommended that you call your local poisons centre for advice, large amounts will require a visit to an emergency centre!

You should ensure that crockery and utensils used for cooking and eating are cleaned in clean drinking water as you will be putting food on these and into your mouth. This is a route of infection known as fomites. Hands can be washed in less sterile water, but you should treat with hand-sanitizer before handling food (either while cooking or eating).

Reference:

  • National Research Council (US) Safe Drinking Water Committee. Drinking Water and Health: Volume 2. Washington (DC): National Academies Press (US); 1980. II, The Disinfection of Drinking Water. Available from: https://www.ncbi.nlm.nih.gov/books/NBK234590/
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  • Good to know re: hydrogen peroxide. Sticking with treatment tablets and boiling - you didn't mention it but I imagine that 1 tablet per liter applies even when treating 20-30 liters at a time (gallons of water)? You noted the need to treat even water for dish washing. Is boiling, letting cool, then storing that cooled water in a tote for dish washing sufficient? After a round of dish washing we would dump the water, but are the totes for rinsing and washing now fomites that need to be cleaned, or can they be re-used with 'fresh' treated/boiled+cooled water?
    – cr0
    Commented Feb 16 at 14:03
  • @cr0 has the tote contained unclean water? If all you’re doing is sterilizing by boiling and then storing in a clean container, the water is clean. If you collected the water in a container, you’d want to clean the container before using it to store now-clean water Commented Feb 16 at 19:04
  • @cr0 Yes, stick to the one tablet/litre. This produces enough hypochlorite to sterilize the water. Boiling for the dishes is fine, or for cooking/drinking in general. There are very few, f any, pathogens that will survive boiling - though there are some toxins produced by pathogens that will survive boiling, but these are mostly produced in food, not water. No, the rinse/wash containers are not generally a risk for fomites, unless you used non-sterilized water in them, in which case the dishes themselves are too.
    – bob1
    Commented Feb 18 at 19:57
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Frame challenge.

Unless you are camping near a considerably polluted stream taking water from it for washing your hands and for washing dishes - especially since I'll assume you'll be using soap/detergent - will be plenty safe.

No additional treatment such as boiling, or chemical treatment is necessary.

If you are really worried then just use a small amount of "treated" water to rinse your washed dishes in the end, that will drastically reduce your water usage.

Depending on where you are it would also be perfectly safe to drink the water as is, but that depends on a few more factors.

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    Re your last sentence: I would not drink untreated water from a "frequented state forest in the Northeast." The high backcountry of the West is one thing; but a frequented area in the Northeast can be frequented by some people who are not familiar with proper wilderness hygene.
    – ab2
    Commented Mar 7 at 0:14
  • Some people forget about the obviously safest way to purify water: just stay at home and use whatever the state provides. You can drink it, bathe in it and even sue if anything goes wrong. Or as a local saying goes: there are bears in the forest.
    – Vorac
    Commented Jul 6 at 10:36

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