Environ. Sci. Technol. 2009, 43, 970–971
Response to Comment on “Point of Use Household Drinking Water Filtration: A Practical, Effective Solution for Providing Sustained Access to Safe Drinking Water in the Developing World” We thank Lantagne and colleagues for their comments (1). We support a broad range of solutions for global coverage by POU technologies and maintain that rational criteria are needed for effectiveness and sustainability. We stand by our analysis as a contribution to the goal of sustained access to a sufficient, continuous, affordable, and safe water supply, and wish to address their criticisms. While we agree that that technology selection “...cannot be completed in isolation from consumer preference, economic considerations, cultural practices, and local water quality,” fundamental and uniform criteria applicable to all situations are an essential starting point for policy-makers and implementers to evaluate options. The commenters state that “flaws include (1) incomplete and vague definitions of the ranking system criteria, therefore making it subject to bias; (2) scores assigned drawn from insufficient evidence; and (3) omission of key sustainability criteria...” We contend our criteria are consistent with the water management goals of the WHO Guidelines for Drinking Water Quality (GDWQ) through Water Safety Plans (WSPs). WSPs require information on and continuous management of source water quality and quantity, appropriate treatment and its effectiveness, and safe storage or distribution. The criteria we identify are essential for consistent good practice, and scores were drawn from the evidence available. Rather than rejecting the criteria, we must improve the current evidence base. We support development of more refined criteria and the gathering of sufficient data to expand the evidence base for scoring and ranking technologies. We now address specific criticisms: 1. Water quality. The commenters are correct that options such as chlorine are effective in treating low-turbidity water. However, we believe the equal emphasis on turbidity reduction and disinfection is appropriate. The current practice of distributing and promoting technologies without specific guidance on when waters are too turbid for them to be effective is inappropriate for good practice. Because excess turbidity reduces the performance of chlorination and solar disinfection, it is essential that clear and consistent guidance be provided on when these technologies are inappropriate and result in microbiologically unsafe water. According to the commenters “research has demonstrated the effectiveness of chlorination in reducing diarrheal disease incidence in populations using turbid waters.” The studies cited are insufficient proof that turbidity reduction is not necessary for effective water disinfection by chlorine or solar energy. Because inadequate disinfection of turbid water has caused increased waterborne infectious disease risks, promoting chlorine or solar disinfection of turbid water without clear guidance should not be recommended. We often lack the necessary information and tools to determine when water is too turbid for effective technology performance. Accessible, simple, and affordable methods for routine measurement of turbidity, free chlorine residual, and UV light absorbance or transmission are needed. 2. Technologies must provide enough water for daily 970
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needs. People who consume both treated and untreated water to meet their daily needs are still at risk of disease. The 20 L per day volume is based on 5 L/person/day for a family of four. This is actually below the WHO GDWQ, which suggest a minimum of 7.5 L/person/ day. We disagree that smaller volumes of water are “sufficient for many families” because they must then use both treated and untreated water, or give treated water only to some family members. Technologies that take >4 h to produce 20 L may be suitable for smaller households, but may only produce the minimum volume required per day for a household of multiple adults and children. Household members may consume untreated water to meet their minimum needs, putting them at risk for disease. We agree that the exact time frame is open for discussion and further consideration in the context of meeting a household’s minimum daily water needs. However, we consider 20 L in four hours appropriate until there is good evidence to the contrary. We acknowledge that more detailed approaches to cost and economic sustainability are desirable, but their complexities are beyond the scope of our analysis. There have been more rigorous economic analysis of POU technologies, but we believe our simplified analysis comparing single-use/consumable, multiuse, semidurable, and durable technologies on a simple cost-perliter basis provides a simple but rational starting point for evaluating affordability for households and communities. The supply chain criterion did not “deliberately leave out a key link”. We focused on one aspect: the need for a continuous supply of or access to the technology. For this part of the supply chain metric, objective data are actually available. While we agree with the importance of “logistical components necessary to make the technology available to the user by implementers”, we are unaware of available, objective data allowing for assessment of difficulty in transport from suppliers to consumers. Incorporating this into future criteria as studies become available is desirable. Regarding the second point about decreased ceramic filter use due to breakage and difficulty in accessing replacement filter elements, publication of our analysis prompted implementers to address these problems under various business models (http://www.wsp.org/UserFiles/file/ 926200724252_eap_cambodia_filter.pdf). Both “objective” and “subjective” indicators are appropriate to evaluate POU performance and sustainability. Differentiating between objective and subjective indicators may be appropriate as criteria evolve. However, suggesting that only technologies providing measurable chemical residuals can be reliably assessed for sustainability introduces different reporting bias. In our filter studies, we used the most objective assessment criteria possible, which are not restricted to self-reported use. Observations included measurements of microbial quality and turbidity, as well as visual inspection of filters. Furthermore, self-reporting coupled with observations are standard and accepted methods of assessing sustained use in handwashing and latrine studies, for which such observations have addressed and overcome potential respondent bias. We disagree that a definition of sustained use requires a “standardized” time period after technology introduction. We believe it is necessary to track sustained use over increasing periods to determine if use changes 10.1021/es8026133 CCC: $40.75
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over time and why. Such data are woefully lacking for all technologies, especially from independent postimplementation assessments of the kind we report on filters. 7. The unpublished biosand filter studies cited are currently in press or undergoing peer review. One will be published as a peer-reviewed WSP Field Note, as was the previous ceramic filter study in Cambodia. The biosand filter research by Stauber (2007) has been accepted as a peer-reviewed article in the American Journal of Tropical Medicine and Hygiene. 8. We regret that the Parker et al. paper citing 71% sustained hypochlorite use was not referenced, but do not believe it contradicts our conclusions. The study found 71% of 51 households having detectable chlorine residual at 1 year post-intervention. However, this was only about half of the original 98 study households assessed at 2 weeks post-intervention. In our sustainability studies of the biosand filters, study households lost to follow up were counted as nonusers of the filter. It is unclear how the households lost to follow up might alter sustained use rates in the study, if they were counted as nonusers as we have done in our studies. Furthermore, we have since found other CDC studies of hypochlorite continued use rates that were far lower (http://www.who.int/household_water/resources/ Freeman.pdf). We stand by the criteria and scores as consistent with available data, but appreciate the need to revise and expand as new data become available. We encourage studies that
will contribute to a larger evidence base that informs these sustainability criteria and scores. Because each of the commenters is primarily or exclusively engaged in developing, promoting, and/or analyzing a specific HWT technology (chlorine, coagulant-flocculant-disinfectant, or solar disinfection), we welcome their involvement in improving and expanding the performance criteria and commissioning independent post-implementation assessments of their performance. We urge all stakeholders to contribute to the further development and use of robust, broadly applicable criteria for evaluating POU sustainability. We believe the framework presented here provides a valid and useful starting point.
Literature Cited (1) Lantagne, D. S.; Meierhofer, R.; Allgood, G.; McGuigan, K. G.; Quick, R. Comment on “Point of Use Household Drinking Water Filtration: A Practical, Effective Solution for Providing Sustained Access to Safe Drinking Water in the Developing World”. Environ. Sci. Technol. 2009, 3, 968–969.
Mark D. Sobsey, Christine E. Stauber, Lisa M. Casanova, Joseph M. Brown, and Mark A. Elliott Department of Environmental Sciences and Engineering, University of North Carolina, Chapel Hill, North Carolina 27599-7431 ES8026133
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