Straining and Filtration

Straining water through a piece of clean cloth is an extremely simple, low- resource method and widely used for household water treatment. Cloth filters have been used in many cultures for centuries. Typically in South Asia, a sari or saree (a strip of unstitched cloth ranging from four to nine meters in length that is draped over the body of women (it is also a traditional garment) is folded 7 to 8 times and used as a filter. In laboratory experiments using electron microscopy, it was found that an inexpensive sari cloth, folded four to eight times provides a filter of about 20 µm mesh size, was small enough to remove all zooplankton, most phytoplankton, all Vibrio Choleraeattached to the plankton and other particulates larger than 20 µm (COLWELL ET AL 2003, SWIC N.Y.).

The risk of cholera is therefore reduced of about 50% (HUQ et al., 1996).Water is poured through the folded sari cloth and collected in a pot underneath. The efficiency of straining depends on the weave of the cloth and the number of times it has been folded. Specific monofilament filter cloths are very efficient where guinea worm disease is prevalent. Such cloths remove organisms known as copepods, which act as intermediate hosts for the guinea-worm larvae. Dracunculiasis, more commonly known as guinea worm disease, is caused by drinking water hosting a parasite called Dracunculus medinensis (DPD 2008).

Effectiveness of straining. Adapted from CAWST (2009) 

In a laboratory experiments, it was found that an old sari cloth made up of cotton is most effective in removing V. Cholerae. After several launderings, threads of an old sari become soft and loose, reducing the pore size compared to a new sari cloth (see pictures above) (COLWELL et al. 2003). Cloth filters do not remove chemical contaminants or dissolved compounds from water. After straining, additional treatment methods can further improve the safety of drinking water.