All-
No, No, No! Storing water in a dark container does NOT kill pathogenic
bacteria or other organisms! Nor does refrigeration or even freezing. E Coli
and other bacteria can survive for weeks in a cold dark environment. Heating,
filtration, UV disinfection and chemical treatment (chlorine or other) are the
only recommended methods I'm aware of for drinking water decontamination.
Bacteria tend to cling to particles in the water so allowing it to settle or
adding a flocculating agent can sometimes help a little. Particulate material
in the water also blocks UV penetration and thus makes solar (UV) disinfection
less effective.
Part of the problem with bore wells and similar systems is that they become
readily contaminated by misuse and need to be monitored. I'm aware of a
diarrheal outbreak in Kenya caused by a contaminated well, and so we recommend
frequent testing of community water sources. We supply the testing materials
to trained health workers and others at no cost so that they can safely and
accurately monitor local water supplies. For the average family it's better
to just assume contamination and develop the habits of drinking water
purification.
The WAPI's (Water Pasteurization Indicator's) that Jeff Holiman and others
mentioned cost $7.00 each on the Solar Cookers International website, but
really only cost about $.05 to manufacture. Where the rest of the money goes,
I know not. Bob Tait of Clackamas, Oregon makes and distributes thousands of
them for free to various missionary groups and other non-profits. My only
point with Bob is that I believe they should used as part of a general program
that supports various health and sanitation practices including safe latrines,
hand washing and clean water storage. These practices can be adapted to local
cultural practices and should include follow up and support.
Our free training programs include teaching accurate testing and interpretation
of water samples using the 3M petrifilm methods and a second fluorescent
confirmatory assay called Colilert. We also train participants in the use of
the WAPI's, and other disinfection methods and in the construction of simple
solar and biomass stoves that that families can use to heat their water and to
cook. The workshops usually take a day and a half but for efficiency sometimes
can be squeezed into a day. If there is enough interest I could organize one
here in Portland or in some other site.
Tom Carter
________________________________
From: Crispin Pemberton-Pigott <[email protected]>
To: 'Tom Carter' <[email protected]>; 'Discussion of biomass
cooking stoves' <[email protected]>
Sent: Thursday, February 14, 2013 11:59 AM
Subject: RE: [Stoves] A simple water sterilization technique
Dear Friends
Keeping water in the total dark for 3 days kills quite a lot of things
including Bilharzia. When I worked in Rural Water Supply in Swaziland we
provided covered tanks with more than 3 days storage on most systems for this
reason (in the lowveld). We also used dosing boreholes with chlorination
occasionally (always when new) and precautionary chlorination using bypass jets
on pumped systems to get a 2 ppm level at the last standpipe. No one boiled
water to purify it in those days.
In contrast, nearly everyone in peri-urban and rural Indonesia boils their
drinking water. Completely different situation, for which stoves are required.
Regards
Crispin
Jeff-
Thanks for the post. Yes, it's true that pasteurization at 65C kills all
pathogenic bacteria and viruses, as well as worms and cysts. I don't recommend
"feeling it with your hand" however as even a 10 degree lower temperature will
have a much lower effectiveness. As you note, a wax indicator developed by Dr.
Robert Metcalf accurately and safely demonstrates when the water is pathogen
free. We distribute them at no cost to families and instruct them on their
use. Filtration through a clean cloth probably helps a little, as does letting
the water settle, but is not necessary for pasteurization. Some methods that
use solar UV disinfection do require clean water and clear PET water bottles
for effectiveness. They also take longer, lack an end point and have
inconsistent results and for that reason we don't recommend them.
The last step is keeping safe water safe, by storing it in clean containers
with small openings so that people cannot recontaminate it by dipping in with
dirty containers or hands.
I'm going to give a water testing and water pasteurization workshop here in
Portland in the next months if anyone is interested in being trained.
Tom Carter
Agua Pura Para El Pueblo
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