Clothes clean drinking water
Filtering with an old sari cuts
cholera cases by half.
14 January 2003
KENDALL POWELL
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| Saris have long been used to
filter insects from drinks |
| © Getty Images |
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Filtering drinking water from rivers and ponds through a
folded piece of cotton cloth could cut disease by half in
cholera-plagued countries, a new field study suggests.
Cholera causes acute watery diarrhoea that can lead to severe
dehydration and death in infants and the elderly. The World
Health Organization recorded about 124,000 cholera cases last
year alone, and 3,800 deaths.
Putting water through an old piece of sari - the traditional
garment worn by women in India and Bangladesh - folded at least
four times halved cholera cases in 65 Bangladesh villages during
a year and a half, researchers found1.
"We were thrilled. I certainly expected a reduction, but to
get a 50% reduction was wonderful," says study leader Rita
Colwell of the University of Maryland, College Park, director of
the US National Science Foundation. The researchers taught
villagers how to fold the cloth, rinse it in filtered water and
dry it completely in sunlight after use and why this might
prevent disease.
The trick takes advantage of special properties of the
bacterium that causes cholera, Vibrio cholerae. The bacteria are
tiny and would on their own be impossible to strain out with a
simple filter. But they hang onto the egg-cases and mouths of
copepods - microscopic crustaceans a thousand times larger than
the bacteria.
Also, whether or not a person becomes sick depends on how
many bacteria they swallow. So reducing the level of bacteria in
drinking water, even without eliminating them completely, cuts a
person's chance of becoming seriously ill.
"These bacteria are in water sources because that's their
habitat. You are not going to be able to get rid of them," says
microbiologist Jay Grimes at the University of Southern
Mississippi in Hattiesburg. "You have to try cleaning the water
before people consume it, and this is by far the simplest thing
you could do."
Boiling is the most effective way to purify water, but in
Bangladesh, wood for fuel is scarce. Many villagers rely on
rivers, lakes, and ponds for household water - especially
because many drilled wells have become contaminated with
arsenic.
Cheaper is better
Anwar Huq, an environmental microbiologist at the University
of Maryland Biotechnology Institute in Baltimore, explains how
the group decided on sari cloth: "Being Bangladeshi, I had seen
people using old sari cloth to filter insects out of a sugar
drink made in the home."
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| Old, cheap sari material
(bottom) makes a better filter than new, expensive
cloth (top). |
| © R.R. Colwell et al. |
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In lab tests the researchers found that old, cheap sari cloth
makes a better filter than new, expensive cloth. The threads
become smushy and loose, as a result the pore size becomes even
smaller," says Huq. "It really works, and it doesn't cost a
penny for poor villagers to use." Filtration might help to fight
other waterborne diseases, such as dysentery and salmonella, he
suggests.
Low-tech filtration might get a high-tech boost from
satellite imagery to help combat Bangladesh's autumn cholera
outbreaks. A rise in water temperature in the Bay of Bengal
results in a plankton bloom. This causes a growth spurt of
copepods, each of which can carry up to 10,000 cholera bacteria.
Satellite water-temperature data could warn of an impending
outbreak so that extra measures, such as treating water with
chlorine pills, could be taken in those months. |
