Testing for Reliable Bacteria Reduction

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Hand-held individual water purifiers (IWPs) are commercially available and have been used by the military since World War II. Because of variations in water quality and assumed usage patterns, and because of the lack of accepted testing standards, manufacturer performance claims have sometimes proven to be unreliable indicators of device effectiveness.

The U.S. Army Center for Health Promotion and Preventive Medicine (USACHPPM) received a grant from the Army Study Program Management Office to develop a protocol for products with such claims, NSF Protocol P248, Emergency Military Operations Microbiological Water Purifiers. USACHPPM received assistance from NSF Intl. and from many other DOD organizations. The protocol was derived primarily from publications of the U.S. Environmental Protection Agency (EPA) and NSF Intl.

Using surrogates, the requirements under the protocol are a 6-log reduction of bacteria; 4 log for virus; and 3 log for cysts. Because it is impractical to test with a continuous concentration for all organisms for the full test volume, performance is evaluated at microbiological challenge points during the test capacity. The protocol requires greater concentrations of bacteria than would be anticipated in source waters because these concentrations are necessary to determine the required log reductions. To represent field use, a bacterial “background” concentration for use between sampling events that more closely represents natural water conditions was developed.

The protocol applies to “natural water,” defined as any body of water, standing or flowing, which is sufficient for a service member to use as a personal water supply. Available data, primarily derived from public water sources such as lakes, large rivers and reservoirs; recreational waters; and wadeable streams was reviewed to determine the bacterial quality of natural waters.

The intent was to determine conditions under which an IWP must operate. The sources for this research include a number of scientific journals, the EPA, the U.S. Geological Survey, the European Environment Agency, United Nations Environment Programme-Global Environment Monitoring System Water Programme and the World Health Organization (WHO). Source water standards exist in reference to recreational water safety and agricultural/fishery health impact. The EPA, EU Environment Programme and the WHO recommend maximum concentrations as shown in Table 1.

The comparison of the relative bacterial qualities of waters in different locations is based on the detection of indicator organisms. Total and fecal coliform are the most commonly used indicator organisms; they are the ones stated in regulations for water use classification (Table 1); and they provide an estimate of the pathogenic bacteria present in natural waters. Limited research was conducted to determine the ranges of total and fecal coliform concentrations in natural waters worldwide indicated (tables 2, 3) that total coliform bacteria detected ranged from non-detect to 500,000 cfu/100mL. From this information, a background concentration of 1,000 to 10,000 (103 to 104) cfu/100mL was set as the concentration of bacteria to be introduced to the device continuously during non-sampling periods. This concentration creates the conditions that the device will encounter during actual field use and indicates the ability of these organisms to “grow through” the device’s bacteriological barrier.

Table 2 shows the ranges for each organism found within the indicated body of water. As shown, concentrations vary considerably, indicating the effect that environmental or seasonal conditions have on water quality.

Water treatment facilities in the U.S. use raw water quality information to determine appropriate treatment strategies for compliance with EPA drinking water regulations. The Information Collection Rule of 1996 required the EPA to compile data on the presence of certain microbes in addition to indicator organisms in drinking water sources. A summary of these is shown in Table 3.

Nikki Beetsch is the business unit manager for NSF International’s Engineering & Research Services group. Beetsch can be reached at 800.NSF.MARK or by e-mail at beetsch@nsf.org.

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