Water and Water Filtration
They say travel broadens the mind. It's also fair
to say it loosens the bowel as well, something you can do by tucking
into dodgy food, but just as easily by drinking unsafe water. My attitude
to upland water always used to reasonably cavalier. I heeded the common
sense advice about not taking water below farms, but higher up, I'd
be quite happy to dip my hand in a stream for an on-the-move slurp without
a second thought. The first time I did take a second thought was as
I set off on a two week coast-to-coast backpack across the Scottish
Highlands, three days after a certain nuclear reactor in the Ukraine
showered Western Europe with radio-active fallout.
Official opinions on slurping water directly from upland streams and
rivers in the UK are fairly non-committal, but certainly the view from
the National Rivers Authority is that you shouldn't be lulled into a
false sense of security by drinking water in a wilderness location.
"Pesticides get into the water by all sorts of diffuse means,"
I was told, "and it doesn't necessarily mean that just because
there isn't a pipe dumping them straight into the water that they aren't
Many prime walking areas overseas have become victims of their own popularity.
Mountain streams in many parts of North America, for example, now harbour
giardia cysts, directly attributable to human activity. So just what
are the dangers of drinking with gay abandon from water sources which
may not be as wild and as pure as you think? Some can be seen, others
not. They're measured in microns (1/1000th of 1mm), and just to give
you an idea as to how far you should be straining your eyes, if not
your water, the full stop at the end of this sentence is about 500 microns.
Everything from dirt and sediment (the fine "flour" in glacial
rivers is one of the fastest working laxatives around), rust, scale
and radioactive particles - 100 microns +
Removed by: filtration, or allowing suspended particles to settle
Cholera, Salmonella, Escherichia Coli, Typhoid - 0.2-10 microns
The list of nasty things you can pick up from bacteria is as long as
a roll of toilet paper. Pneumonia, food poisoning, intestinal fever
and dysentery are just some of the delights in store for those who drink
Removed by: microfiltration, boiling or chemical treatment.
Giardia, Cryptosporidia, Entamoeba - 5-15 microns
Undoubtedly the most infamous is the Giardia cyst - responsible for
the majority of water-borne illnesses in North America. It survives
as a tough-walled cyst for months in water. Drinking as few as six can
cause infection, and when they reach the gut, they rapidly break down
to produce up to a million baby parasites within 10 days. The classic
symptoms are abdominal cramps, diarrhoea, vomiting, and what the Americans
politely call "gas" - both ends!
Removed by: microfiltration, chemical treatment or boiling.
Polio, Hepatitis A - 0.004-0.1 microns
The smallest nasties to be found in water, and undoubtedly the most
dangerous. If you're travelling in third world countries where these
diseases are prevalent, then you'd be unwise not to have been immunised.
But there are other water-borne viruses which can cause diarrhoea, flu
Removed by: though they often attach themselves to larger hosts,
the smallest can't be guaranteed to be removed by filtration. They have
to be killed off either by boiling, or by chemical treatment - chlorine
Pesticides, fertilisers, diesel fuel, heavy metals from mines
More likely to be found in lowland areas, but not exclusively so.
Removed by: activated carbon will remove organic chemicals by
adsorption, where the molecules stick to the carbon - but not dissolved
Boiling kills off all water-borne pathogenic
organisms. Trouble is, you have to maintain the water at a rolling boil
for 5 minutes - an extra burden on your fuel supplies. It's further
complicated by the fact that boiling temperatures decrease with altitude,
dropping 5 degrees C every 5,000 feet. At 15,000 feet - not untypical
for some Himalayan treks - a boiling temperature of 85 degrees C won't
guarantee to kill off hardier bugs.
Apart from the resultant taste, chemical tablets work fine, but they
don't clean the water, and they do need to be left long enough to work
properly. Filter/purifiers are the best option for speed and convenience.
Some companies make gravity-fed filters, but their flow rate can be
painfully slow compared to the pump-action models featured here. The
flow rate figures are variable dependent on the quality of raw water
available. Suck up water from a pool of sludge, and you'll do your filter
in very quickly. If, on the other hand, you're selective, taking water
from a clear source, using the float where provided to keep the intake
tube out of any sediment, you'll prolong the life of the filter considerably.
Some manufacturers quote a finite life for
their products in terms of a maximum volume of water treated. I haven't
repeated them here simply because there's no way of knowing what water
quality they're based on, and in some instances the figures aren't even
It's all too easy to become pre-occupied with
a filter's performance where the contamination is something you can
see. What counts is how it handles the nasties that only show up under
an electron microscope. Short of taking the whole lot to a public health
laboratory, I've worked on the basis of supplied technical data, and
judged the different models on their ease of use, and the palatability
of the filtered or purified water. In fact, all filter out particulate
matter, cysts and bacteria - those with added iodine provide the only
sure treatment for viruses.
The minimum pore size is what counts when it comes to trapping bacteria
measuring .3 or .4 microns, or larger protozoa and dirt. Filters are
either membrane or surface types, which quickly get coated in gunge
but are easy to clean, or depth filters, made of thick porous materials
like activated carbon or unglazed ceramic. The latter rely on progressive
filtration, and so contaminants move further into the material. Some
depth filters are partially cleanable, either by backwashing, or by
brushing the outer surface.
An additional element of treatment which doses the water with iodine
to kill off bacteria and viruses. In areas where viruses are likely
to be prevalent - notably third world countries with poor sanitation,
this kind of unit provides the best peace of mind. Not everyone likes
the taste of iodine, however, and prolonged use beyond three months
is not recommended. Activated carbon filters will remove the taste of
iodine. The Pur filters can be fitted with an optional carbon cartridge
attachment which does this. If you're using a carbon or ceramic filter
in such risk areas, use chemical tablets as well to be absolutely certain.