Do Gravity-Bag Filters Remove Bacteria and Viruses?

Effectiveness Against Bacteria

Gravity-Bag Filters are designed to remove bacteria from water using a combination of filter media, such as activated carbon and ceramic elements. These filters have a porosity of around 0.2 microns, which is sufficient to catch most bacteria, including E. coli and Salmonella. According to the World Health Organization (WHO), a filter with a porosity of 0.2 microns or smaller can remove 99.99% of bacteria from water.

Effectiveness Against Viruses

Regarding viruses, Gravity-Bag Filters may not be as effective. Viruses are typically smaller than bacteria, with diameters ranging from 20-400 nanometers. While some Gravity-Bag Filters may claim to remove viruses, their effectiveness can vary widely depending on the specific filter design and the type of virus present. For example, a study by the National Sanitation Foundation (NSF) found that a Gravity-Bag Filter with a porosity of 0.2 microns was able to remove 99.9% of Rotavirus, but only 80% of Norovirus.

Common Applications and Pre-Treatment

Gravity-Bag Filters are commonly used in emergency water treatment, camping, and outdoor recreation. To increase their effectiveness, it’s often recommended to pre-treat the water with coagulation or sedimentation before passing it through the filter. This can help remove larger particles and improve the filter’s performance. For example, adding a small amount of alum (aluminum sulfate) to the water can help coagulate particles and improve the filter’s ability to remove bacteria and viruses.