How to make water drinkable

In several occasions will need water when we’re just far away from the “civilization” and from bottled water. In developing countries like the ones in SE Asia the water can have a lot of microbes. Some of them will cause only traveler’s diarrhea, but other ones could cause Cholera, Hepatitis and other more serious diseases. Even when immunized, we must be careful (and I guess nobody want to be all day shitting shit ).

If we need to take water from a river, a lake or even a suspect pat we can kill water microorganisms in one of the following ways (short by reliability):

How to make water drinkable

  1. Boiling the water. It’s the most reliable method. We have to boil the water at 100 ºC (212 ºF) for 1 minute, but water boils at different temperatures depending on atmospheric pressure and that depends on elevation and ambient temperature at the same time. As a general rule we could say the water boiling point is reduced 3 ºC each 1000 m of elevation so for an appropriate purification we must boil the water for 3 minutes and let it cool down at ambient temperature. If we cannot boil the water we could keep it at least at 60 ºC (140 ºF) for longer time, although it’s not so effective.
  2. Filtration. There are 3 types of pathogens we have to protect against:
    OrganismExamplesGeneral SizeFilter TypeParticle Size Rating
    ProtozoaGiardia, Cryptosporidium5 microns or largerWater filter1,0 - 4,0 microns
    BacteriaCholera, E. coli, Salmonella0,2 - 0,5 micronsMicrofilter0,2 - 1,0 microns
    VirusesHepatitis A, Rotavirus, Norwalk virus0,004 - 0,06micronsWater purifierdown to 0,004 microns
    Source
    Although there are 2 basic types of filters (membrane and depth), both can be either water filter or water purifier. Water filter cannot remove a lot of viruses since they only filter out particles up to 0,1-0,2 microns generally. Water purifiers do filter out viruses.

    • Depth filter use thick porous materials such as activated carbon or ceramic to trap particles as water flows through them (they use the adsorption capacity of those materials). They are easier to crack (don’t be clumsy), but can remove several heavy metals and chemicals from the water (including iodine). They use to be water purifiers rather than water filters. Some examples are Lifesaver (purifier), Katadyn (purifier) and Grayl (filter and/or purifier).
    • Membrane filters use thin sheets with precisely sized pores that prevent objects larger than the pore size from passing through. They are easy to clean but clog quicker. A well-known (sensationalist) example is Lifestraw (be careful, it’s a water filter, not a water purifier).

    Filters have a disadvantage: they have a short life and are expensive. They have to be replaced every now and then (as the manufacturer says) because they end up clogged and also in order to avoid the microbes’ remains be used for feeding other microorganisms becoming the filter a source of microbes. Good purifiers use to have a biological agent which destroys those remains.

  3. Chemical treatment using iodine or chloride. This method has some disadvantages:
    • 30 minutes are needed after dissolved to take effect.
    • The cloudier the water, the less effective. It should be filtered at least with a cloth to remove large particles.
    • The colder the water, the less effective. Water should be above 25 ºC (77 ºF) and if it’s not possible, at least 16 ºC (60 ºF). Below 5 ºC (41 ºF) for iodine and 10 ºC (50 ºF) for chloride, double the treatment time.
    • The water has a bad taste after using them. It can be solved using additives when purification is finished (after the 30 minutes) like Vitamin C.
    • Iodine is more effective than chloride, but it shouldn’t be used for longer than few weeks due to its toxicity for the thyroid gland. It can be harmful for people with thyroid problems, women over 50 years-old, pregnant women and people who are allergic to iodine (like those who are allergic to shellfish).
    • Treatment with chloride (less effective with protozoa) can be done with sodium hypochlorite (NaClO), that’s bleach (well, bleach is that diluted in water). The bleach must be pure, without detergent or perfume or with an ad where it’s said it can be used for disinfection of consumption water. In the following table are indicated the doses must be used depending on its chloride concentration (normally bleach has around 5% concentration of sodium hypochlorite what’s equivalent to add 1 or 2 drops of bleach to the water):
      Volume of water to treatConcentration of the used bleach
      20 gr. chloride/liter40 gr. de chloride/liter80 gr. de chloride/liter100 gr. de chloride/liter
      2 liters4 drops2 drops1 drop1 drop
      20 liters20 drops10 drops5 drops4 drops
      100 liters5 ml2,5 ml25 drops20 drops
      1000 liters50 ml25 ml15 ml10 ml
      Source

  4. Purifying using UV light. It’s more and more frequently used for bottling and big purifiers due to its odorless and tasteless effect in the water. However, the water must be clean so that the UV light can reach every single point. Thus, water must be filtered previously if it’s too much turbid.

    When traveling we can use one of the following options:

    • Solar disinfection using UV light from the sun. It’s named SODIS method, approved by WHO as an effective method to purify water in developing countries, and it’s essentially to set PET bottles out in the sun on a dark surface for 6 hours. Well, that’s the same as when you forget the water bottle in the car. Don’t you feel like now that great hot purified water?
    • UV light devices like the portable emitter SteriPEN. Its efficacy is not 100% proven but it appears to be working (I wonder if the power emission is enough…). In the ads the device is inside a transparent glass but if I were you I wouldn’t do it like that. Firstly because it will be more effective if the light can bounce and secondly because UV light destroys organic particles; that’s also your skin. Although I think the low power of that will only make you look more tanned.
  5. Chemical treatment with silver ions. Actually it’s not approved by WHO as an effective disinfectant but I put it here due to 2 reasons: because it’s more than nothing in case of emergency and, specially, because I’ve seen it sold like the ultimate method to kill microbes in any water, even in big companies like Decathlon, and IT’S NOT. So be careful and check carefully the composition of any purification tablet you find. Silver ions tablets are not reliable.

We can also mix methods. For example, we can use a water filter to filter out most of the particles and then use iodine/chloride treatment or UV light emitters to purify the filtered water. That way we boost the effect of both methods.

I also recommend to read this chapter of The Backpacker’s Field Manual by Rick Curtis, this comparative by Eytan (SnarkyNomad) and between filters and purifiers and this article (in Spanish) by AMSE (Spanish Medical Asociation of Overseas Health). And if you want anything deeper, you can have a look to the WHO recommendations (World Health Organization) wink

Finally, it’s advisable to have a backup method. I’ve bought a Grayl system with filter and purifier but I’m also carrying iodine or chloride tablets.



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