How many of you are nervous about the water you drink
when walking or trekking? In some places it is a valid worry as there are potential ‘nasties’ lurking in impure water that can lead to illnesses,
including travellers diarrhoea. The germs that cause the problems are, in order
Protozoa and cysts -
parasites or cysts . e.g. Giardia and
Cryptosporidium. Can be found in UK and
Ireland but is most likely in developing countries
Bacteria - E.coli, cholera,
salmonella, typhoid and dysenter
Viruses - Hepatitis A
Contaminated water is often blamed unjustly and proper
hygiene is just as important, unclean hands can often transfer pathogens to
food or water.
What is the source?
Choose carefully, even mountain streams may have villages
above them and lowland agriculture and industry use herbicides, pesticides, and
fertilizers. Dirty water is unpleasant to drink and the bits can upset your
stomach. The bits also reduce the effectiveness of the methods for creating
safe water. If the water has bits in it, let it settle for an hour or more and
siphon off the clear water. To clear larger debris pour the water through
finely woven cloth, a coffee filter, a sand filter made using a sock or a
ceramic filter with a pre-filter on the intake hose to eliminate larger
Choosing the best method to clean water depends on the
amount you need, the source, time, cost and the equipment carried.
When you treat water in a container with a lid, be sure to let some of the treated water clean the threads of the cap and rinse the bottle with clean water between uses.
Bottled Water –
Bottled water creates a waste problem and
should be avoided! If you must drink bottled water, carbonated is best, because
the acidity will help to kill any germs.
When you have the time and fuel, heating water to
65°C for a few minutes kills all germs including Cryptosporidium and Giardia
cysts. Water that is brought just to a boil is safe and boiling for longer,
even at high altitudes, simply wastes time and fuel. Avoid boiled water in ‘tea
houses’ as most use trees as a source of fuel. Other technologies make boiling
water largely unnecessary.
UV light –
impart any taste to the water.
Four Alkaline AA batteries purifies 10-15L, Lithium batteries 65L, and NiMH
75L. However its effectiveness is lower in dirty or icy water (see
above), if the water clarity is poor filter it first or give it three doses of
UV. The downside is that it is expensive, the quartz lamp can break, they are
relatively heavy and batteries run out. The UV tube wears after 5000 uses, but
can be replaced by the manufacturer.
The ‘steriPEN’ uses UV light to destroy the DNA
of germs rendering them harmless, and does not
Chemical purification -
Chemical purification can cheaply
treat a large volume of water while you occupy yourself with more important
tasks. Boiling, filtering or chlorine dioxide are the only ways to eliminate
Giardia and cryptosporidium.
Iodine tincture and chlorine
– These eliminate bacteria and
viruses but not Cyclospora and cryptosporidium cysts plus they need over an
hour to eliminate Giardia especially when the water is cloudy or cold. If you
are in a hurry, double the dose and halve the contact time.Iodine and Chlorine
both flavour the water, but neutralising tablets or vitamin C will remove the
taste, but add them onlyafter the contact time as they will deactivate
them. Iodine is also a useful antiseptic and a drop or two on a leech soon
makes it drop off. Although iodine is rapidly cleared from the body, you should
not use it if you have an allergy to iodine, active thyroid disease, or are
pregnant. Some literature suggests using iodine for six weeks or less, because
of this iodine tablets are no longer sold in the EU, but Iodine tincture is
available through some chemists.
Chlorine dioxide (ClO2) -
Cryptosporidium. ClO2 also,
destroys sulfides, cyanides, and phenols, controls algae, and neutralizes iron
and manganese ions. A 4-hour wait time is required to eliminate Cryptosporidium
from cloudy, cold water. Chlorine dioxide is available in both tablet and
Chlorine dioxide is extremely
effective and rapidly kills everything including
The rational behind using filters is to clear
the water of larger protozoans including cryptosporidium, bacteria, sediment
and organic debris, thus allowing lower doses of halogens to be used to kill
viruses more rapidly. They work by trapping pathogens in a micro-porous screen,
but some viruses are too small to trap. Ceramic filters have a long life (2000
litres) and can be cleaned many times before the cartridge needs replacing. A
pre-filter helps reduce clogging. Ceramic filters can come with a carbon core,
to remove chemicals (but not viruses) from water e.gMSR mini works. Some filters have both a filter and achlorine/ iodine-resin
element that is capable of killing all viruses, but contact time with the
iodine is limited. There are also some lightweight straw and bottle filters but
if the water is dirty then they block in next to no time. There are also
gravity-fed filters to filter the water without pumping.
Filters provide immediate access to small amounts of water
without adding any taste. However, they are expensive, bulky and cracks created
by freezing or erosion may allow the passage of unfiltered water, they can
become contaminated and most do not remove virus particles.
So what do I actually do?
In general, gravity-fed or pump filters, work
faster than chemical treatments, though chemical treatments are lighter and
Day hikes - In Ireland I simply carry
enough water, but if I am travelling lightweight or overnighting where I am a little concerned about the water source I use chlorine or Iodine or my SteriPEN
day hikes - I carry Chlorine dioxide
when I am unsure about the source or filtration combined with Iodine/chlorine.
When I want to treat a lot of water, or there are
limited water sources pump filters or gravity-fed filters work well.
Boiling is fool proof
when you have enough time and fuel.