Can I Drink That?
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STUDY HELPS WARFIGHTERS CHOOSE INDIVIDUAL WATER PURIFIERS.
Warfighters need ample supplies of safe, drinkable water to fight and win on the battlefield. In cases where they do not have access to military-provided drinking water, they must rely on emergency individual water purifiers (IWP) to meet their drinking water needs. Current military-issued emergency water purifiers work slowly, and may produce microbiologically unsafe water. Commercial vendors have marketed alternate purifiers to the military, but none have been systematically tested by the U.S. military.
To better protect warfighter health, the U.S. Army Center for Health Promotion and Preventive Medicine (USACHPPM) recently performed an in-depth performance and health risk assessment of commercial off-the-shelf individual water purifiers in order to develop simple, direct recommendations for the warfighter. The USACHPPM has presented the results of this study, as well as a web-based interactive decision tool, at http://usachppm.apgea.army.mil/WPD/.
PROBLEM BACKGROUND
Currently fielded individual water purification options for the warfighter include iodine tablets and chlor-floc tablets. Neither of these methods fully meets the needs of modern warfighters in terms of ease of use, volume of water produced or confidence that the final product is microbiologically safe. Many small, hand-operated water purifiers, including both filtration- and disinfectionbased devices, have been commercially developed in recent years for campers and hikers.
Although military units have used unit funds to purchase commercial purifiers for deployments, and in some cases individual warfighters have even purchased their own purifiers, their selections have been based primarily on packaging and marketing, rather than a science-based, systematic assessment of device performance in military circumstances. Lack of such an assessment has placed the warfighter at risk of contracting waterborne diseases through the ingestion of waterborne pathogens. USACHPPM recognized this risk through the many requests from deployed units and individuals for recommendations. Its resulting assessment was sponsored by the office of the Deputy Assistant Secretary of the Army for Environment, Safety and Occupational Health and funded by the Headquarters Department of the Army’s Army Study Program.
RESULTS
To be useful and to protect warfighter health, an IWP must provide safe drinking water. In evaluating the safety of IWP-produced drinking water, the USACHPPM study made exposure assumptions regarding population and duration. The study team assumed that only a deployable military population would use the IWPs, and that this population would only use them infrequently and for short periods of time. Based on these two assumptions, the most significant risk to warfighter health in using an IWP is the risk from ingesting water-borne microbial pathogens. Thus we evaluated an IWP’s ability to provide safe drinking water in terms of its ability to reduce the number of active pathogens in water to a safe (non-infectious) level.
To measure this ability, we used the test protocol metric widely accepted in drinking water science and in the drinking water industry— that a safe level of pathogen removal equates to 6-log (99.9999 percent) removal of bacteria, 4-log (99.99 percent) removal of viruses, and 3-log (99.9 percent) removal of parasitic cysts. Thus a “best” IWP should meet this pathogen removal metric. This study found that few commercially available IWPs could meet this metric. Most commercial IWPs reduce pathogens based on one of two primary mechanisms—either filtration or disinfection. Each has inherent technology limitations to meeting the “best” pathogen reduction metric.
Filter-based IWPs reduce pathogens in water through size exclusion. They generally do well at reducing the larger pathogens, bacteria and cysts from water, but do not reduce the smaller viral pathogens to safe levels. Many filter-based IWPs evaluated in this study could successfully remove bacteria and cysts. A small number also showed promise of viral reduction through adsorption on a proprietary filter medium, but require further independent testing to verify the capability. One filter-based IWP was commercially packaged with disinfectant drops as a second purification step, and successfully met the “best purifier” pathogen reduction metric.
Disinfectant-based IWPs kill or inactivate microbial pathogens in water, thus rendering them non-infectious. Chemical disinfectants generally reduce bacteria and viruses well, but struggle to reduce the tougher, more chemically resistant parasitic cysts to safe levels. Even at high chemical dose and long treatment time, IWPs based on chlorine or iodine could not safely reduce the toughest of the pathogens, cryptosporidium. However, at proper dose and treatment time, the chlorine dioxide-based IWPs could kill cryptosporidium and meet the “best” IWP metric for pathogen reduction.
Beyond reducing pathogens, a “best” IWP also had to be small and lightweight; purify quickly; purify turbid (cloudy) waters; not make the water smell or taste bad; be simple to use; and be durable under field conditions. The study found that choosing a “best” IWP involves inherent trade-offs between these characteristics because no single IWP received a highest rating for each. The required trade-off is usually based on the primary pathogen-reducing technology of the IWP—either filter or disinfectant. For example, disinfectants are inherently small, lightweight, and simple to use, but purify slowly and leave water with an unpleasant chemical smell and taste. Filters purify quickly and can reduce bad tastes, odors and turbidity, but are bigger, heavier and more complex to use than disinfectants.
Overall, the study team assessed 68 IWPs produced by 27 different manufacturers. Of these, 53 used filtration as the primary means of pathogen reduction, and 15 used disinfection. USACHPPM has packaged and presented the assessment results as a Web-based IWP decision tool to help warfighters make IWP choices that better protect their health. This decision tool contains a comparative, searchable, relational database of the technical specifications, operating characteristics, and USACHPPM-evaluated pathogen removal capabilities of available commercial IWPs.
DATA COLLECTION AND EVALUATION
To identify and collect IWP data, the study team conducted an extensive market survey of commercially available IWPs that could be purchased by units or individual warfighters. As part of this survey, the team attempted to contact all identified IWP manufacturers to request detailed technical information and performance test data. Manufacturers were informed of the nature of assessment as the basis for the request. Some manufacturers did not respond; for their IWPs, only publicly available product information was collected.
USACHPPM evaluation of IWP pathogen reduction capability was a key part in the development of database information. Laboratory testing results were critical to a high-confidence evaluation of this capability. The study team made deliberate and exhaustive efforts to locate and review all available laboratory test results showing device efficacy at pathogen reduction. The team evaluated the quality of test data based on these characteristics: (1) how closely the testing followed an applicable test protocol; (2) the degree of independent, third-party status of the testing organization; (3) the degree to which testing was conducted in accordance with manufacturer-specified device operating conditions, and (4) the degree to which testing was device-specific, versus based on technology or product family similarities.
EXPERT PANEL SUPPORT AND MULTI-ATTRIBUTE ANALYSIS
As part of the study, USACHPPM also developed specific scenario- dependent recommendations for “best” IWPs. It developed these recommendations through an operational analysis, followed by a multi-attribute decision model analysis performed by two multi-service, interdisciplinary, intradepartmental expert panels. To facilitate the decision analysis, it also added decision analysis experts to the study team.
To verify USACHPPM’s operational analysis and to develop the decision model, the study team first convened a panel of multiservice combat developers, material developers and logisticians as user-representative experts. This expert panel developed a decision model that identified, defined and weighted the 12 most important IWP characteristics required for the “best” IWP. Next, the study team convened a panel of multi-service water scientists, engineers and preventive medicine personnel as technical experts to evaluate IWPs against the decision model. They developed consensus characteristic scores for each IWP. Because there was incomplete data for some IWPs, this expert panel’s knowledge, experience and professional opinions were critically important in technical evaluation to generate IWP characteristic scores.
Overall scores were then calculated using a linear additive approach, in which the converted score for each characteristic was multiplied by its weight, and then summed for all model characteristics.
CONCLUSION
In meeting this project’s objectives, USACHPPM has supported the global war on terror, sustaining a campaign-capable expeditionary Army through providing the means to assess and identify safe, effective commercial water purifiers for emergency individual use. It has also supported Army Transformation by identifying sustainment enablers for the Future Force concept of extended autonomous operations. ♦