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Expedition Skills: Water Sanitation

Updated: Nov 8, 2020


On average a person in a temperate environment needs 3L water/day

In hot environments, this can increase to 15L/day

In addition to this each person typically uses 4L/day for cooking/washing up


To get potable water there are three main aspects to consider:


1. How to Remove Organic Matter

2. How to Remove Silt

3. How to Kill any Organisms






Millbank Bags


Image credit: paulkirtley.co.uk

These finely woven fabric bags can be used to separate organic matter and sediment. Clear water is filtered through the bag into a container below. This is a fairly time-consuming process and the water will still require purification by one of the methods below.




Boiling

Rolling boil for >5mins

Sufficient at any altitude to kill organisms

However depends on fuel/resources etc.

Will not remove toxins/heavy metals




Halogens


Iodine (now not widely available due to EU Biocide regulations)

Chlorine

  • Effective vs multiple organisms

  • Less so via amoebic cysts/giardia

  • Not effective vs cryptosporidium

  • Need to filter first if lots of sediment

  • Water needs to rest for 30mins before drinking; taste!!

Chlorine dioxide

  • Is effective vs cryptosporidium

  • Less noticeable taste

  • More expensive!



Mechanical


Lots of different filters available- remove sediment first (otherwise will slow/block filter)

Types of filter:

  • Ceramic filters (0.2 μm)

  • Microtubules (0.2 μm)

  • Electrostatic

  • Activated Carbon


Some water purification filters use ionised filtration media combined with micro-tubules to remove viruses and in order to remove chemicals an activated charcoal filter is also required.


When choosing a filter, it is important to bear in mind the respective sizes of bacteria, protozoa and viruses as shown in the picture below. The majority of ceramic filters on the market are effective at removing most bacteria, cysts and protozoa but not usually viruses due to their pore size (0.1-0.2 μm).
Bodzek, Michal & Konieczny, Krystyna & Rajca, Mariola. (2019)





Ultraviolet Light

Effective vs. bacteria, viruses & cryptosporidium

Water must be visibly clear

Issues with power/batteries!

Can now get as solar version with charger

Still have to think about chemical impurities



The only way to remove heavy metals/toxins is to use a purification device that includes an activated charcoal filter.




I hope this has been interesting and useful!


Check out our other blog posts to read more about expedition medicine and global health.


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Resources and Further Reading:


Backer HD, Derlet RW, Hill VR. Wilderness Medical Society Clinical Practice Guidelines for Water Disinfection for Wilderness, International Travel, and Austere Situations. Wilderness & Environmental Medicine. 2019 Dec 1;30(4):S100–20.

Bodzek, Michal & Konieczny, Krystyna & Rajca, Mariola. (2019). Membranes in water and wastewater disinfection – review. Archives of Environmental Protection. 45. 3-18. 10.24425/aep.2019.126419.


Johnson C, editor. Oxford handbook of expedition and wilderness medicine. 2nd edition. Oxford: Oxford University Press; 2015. 822 p. (Oxford handbook).