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treating water to make it potable / drinkable


  • one of the main dangers with bushwalking, especially in a hot, dry continent such as Australia, is dehydration from lack of water, high temperatures or gastroenteritis
  • on most bushwalking trails, you should assume ALL water from rainwater tanks and from streams should be treated first to avoid giardia and other causes of gastroenteritis, this is particularly the case if:
    • water is not clear, or,
    • trail is in a high volume hiking region, or,
    • after heavy rains, or,
    • cattle grazing or frequented by horse trail riders
  • potentially fatal leptospirosis 1) can be contracted from drinking river water or stagnant water infected with the Leptospira bacteria from the urine of rodents and other animals - this is particularly a problem after rain or floods, but can be a problem in drought as concentrations increase in stagnant pools (you can also get this infection from splashing the eyes or nose when swimming or canoeing, or into open wounds - don't walk barefoot in high risk muddy areas) - luckily it is treatable with antibiotics, and is rare in Australia - but can be a problem in Queensland and north-east NSW.
  • swallowing as few as 10 giardia cysts might cause someone to become ill (hence even small amounts water such as on the threads of water bottles may be problematic)
    • symptoms usually start 1-2 weeks later
    • an infected person might shed 1-10 billion cysts daily in their feces for up to several months!
    • treatment is usually with metronidazole
  • stomach acid kills many pathogens such as most amoebae but those who take PPIs have much reduced stomach acid secretions and may be more susceptible to gastroenteritis
  • sterilisation effectiveness is generally measured at 99.9% (3-log) eradication
  • if viruses are important then chlorine is the best choice
  • if giardia or cryptosporium then UV or filters are probably the best choice
  • none of these remove chemicals or toxins
    • avoid water with blue-green algae as toxins may contribute to dementia 2)
    • avoid water down stream from industrial factories
  • my recommendations:
    • Sawyer Mini Filter for 1 person hikes as long as no freezing conditions and viruses are not problematic
    • Camelbak UV All Clear or gravity feed filter system for groups where larger volumes water are needed
    • chemical options if long multi-day hikes in cold weather where neither of the above can be fully relied upon
  • your sterilisation efforts WILL FAIL if you are not careful with procedures
    • even a few untreated droplets can give you giardia
    • ensure you do not contaminate the outlet of a filter
      • hand hygiene is important
      • store contaminated inlet tubing separate from “clean” outlet tubing
    • ensure you have not damaged a filter by allowing it to freeze
    • ensure any storage container is first sterilized (unless using chemically treated water)
    • ensure you wipe the rims of the UV steriliser container as this area is not sterilized
    • if the water is cloudy, you should pre-filter it with a 40 micron filter or paper coffee filter
  • sterilisation will not remove chemicals or toxins
  • most filters will not remove viruses but are great for bacteria, cryptosporidium and giardia
  • most chemicals will not treat cryptosporidium but are great for viruses and most bacteria

water treatment options

pre-filtration to remove sediment


  • water should be boiled at least 5 minutes and preferably for 8 minutes
    • 1 minute of rolling boil may be adequate for giardia 3)
  • unfortunately, this requires a stove and pot and uses a lot of fuel and results in boiling water not cool refreshing drinking water


  • giardia and cryptosprodium are 5-15 microns in size
  • bacteria are mainly 0.2-10 microns and are thus adequately filtered by a 0.1 micron absolute filter
  • viruses are usually much smaller than 0.1 microns and require a 0.02 micron filter
  • filtration using 0.1-0.2 micron filters are useful for eradicating > 99% of bacteria and protozoa but not viruses
  • if water is not clear, a pre-filter using 40micron filter should also be used
  • if filtered water is being stored, obviously the storage container MUST be clean and sanitized first (and NOT used with untreated water without sterilization)
  • these units must not be allowed to freeze as this may destroy the filter mesh and you would have no idea if it is working or not until you became sick.
  • Platypus GravityWorks
  • MSR AutoFlow Gravity Filter
  • MSR SweetWater Microfilter
  • LifeStraw
    • designed as a filtered straw for drinking straight from a stream and is very light although sipping can be difficult and it cannot create clean water to take with you
    • not recommended, get the more versatile Sawyer Mini instead
  • Sawyer Mini Water Filter
    • compact, light, great for 1 person hikes
    • 0.1 micron hollow fibre filter, requires regular back washing with supplied syringe to keep clean and maintain flow
    • can be used with a straw, or attached to the squeezable supplied water bladder/water bottle or used in-line
    • a bit slow for larger volumes but is rated at 100,000 gallons!


  • there are many types of chemical sterilisation kits for hiking available and most require 2 hours of treatment, and the chemicals should be stored in a dark environment cooler than 25degC - so not suitable for leaving in the car!
  • cryptosporidium cysts are relatively resistant to chemical sterilisation and ozone but sensitive to UV
  • iodine-based kits taste better but do not kill cryptosporidium cysts
  • most are chlorine-based
    • eg. 4 drops (0.3mL) of 5-6% unscented liquid household chlorine bleach added to 1L clear water and let stand for at least 30min 4)
  • others may be dangerous to the environment if released into waterways

UV light

  • exposure to 5hrs of sunlight is said to sterilise water but this is not practicable for hikers, hence the UV kits which obviously require power but have the advantage of not changing the taste and can be done within 1 minute
  • eliminate over 99.9% of bacteria, viruses and protozoa that cause water-borne illness
  • UV is not so good for viruses (esp. adenovirus, rotavirus, polio, hep A) as high doses of UV is required but these UV kits pump out enough UV dose to even sterilise viruses
  • these do NOT treat the threads of the water bottle so you MUST wipe water off these before drinking
  • do not work with water that is not clear, so you may need to pre-filter it
  • if UV sterilized water is being stored, obviously the storage container MUST be clean and sanitized first (and NOT used with untreated water without sterilization)
  • Camelbak All Clear
    • USB charged lithium ion battery unit screws onto top of Camelbak water bottles
    • 60secs activation whilst constantly inverting the drinking bottle (to allow light to hit organisms hiding behind particles) does 750mL at a time
    • single 4-5hr full charge via the 5-pin micro USB connector can sterilise 60L
    • 230g for the UV unit which appears more rugged than the SteriPen
    • there is a risk of accidentally turning it on in the pack and using up battery
    • optional All Clear pre-filter will also keep the water bottle threads dry
  • SteriPen
    • inserts into drinking bottle (up to 1L and with mouth > 22mm, 90sec minute activation for 1L, 48sec for 0.5L
    • the water sensors must be submerged in the water for the lamp to activate and there must be some mineral content for sensors to detect the water
    • portable, light but a little fragile for hiking
    • should not be used in containers made of quartz or really thin materials, like sandwich baggie
    • “has not been tested against amoebas and therefore we make no claims about its effectiveness against amoebas”
    • optional prefilter which will also keep the water bottle threads dry when immersing bottle in stream
    • Ultra has inbuilt rechargeable battery and can treat 50L water on one charge and weighs 140g
    • Aqua uses 4AA batteries either alkaline (50L water) or lithium batteries (150L) and weighs 80g w/o batteries

distilling salt water

  • as long as the salt water is not contaminated by volatile substances such as hydrocarbons/oils, one can distill the salt water into pure water relatively simply such as:
    • use two bottles on a bed of sand
      • the salt water bottle horizontal on sand which is heated by a wood fire
      • the empty recipient bottle placed horizontally on cold wet sand with its neck attached to the other bottle so the stead will transfer from one bottle to the other.
    • DIY hiking distiller
australia/water.txt · Last modified: 2023/05/23 22:53 by gary1

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