Ceramic Water Filters in Cambodia: a Sustainable Solution for Rural Drinking Water Treatment
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Ceramic Water Filters in Cambodia: a Sustainable Solution for Rural Drinking Water Treatment Joe Brown* and Mark D. Sobsey** *University of Alabama and **University of North Carolina School of Public Health Category: Small Projects. PROJECT OVERVIEW. KEY FEATURES. RESULTS. RESULTS.

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Project overview

Ceramic Water Filters in Cambodia: a Sustainable Solution for Rural Drinking Water Treatment

Joe Brown* and Mark D. Sobsey**

*University of Alabama and **University of North Carolina School of Public Health

Category: Small Projects





Locally produced ceramic water filters are now used by an estimated 100,000 Cambodian households for the treatment of drinking water. Three NGO-managed factories produce and distribute approximately 8,000 filters each month. These NGOs, the Cambodian Ministry of Rural Development, the World Bank Water and Sanitation Programme, and UNICEF collectively sponsored an independent assessment program of the filters currently in use to determine whether filters could be a sustainable solution for drinking water treatment in rural areas. Key research objectives identified by stakeholders were to: (i), evaluate the extent that filters improve microbiological quality of drinking water at the point of use; (ii), evaluate the extent to which filters protect users from diarrheal disease; (iii), determine whether and how filter effectiveness against microbes and/or diarrheal disease changes over time; (iv), determine how long filters are in use in households; and (v), identify factors associated with long-term use and factors associated with discontinuation of use to inform future and current implementation efforts.

This project has resulted in a critical, timely assessment that has been extremely valuable to stakeholders considering further investment in the technology. Findings include evidence of substantial health impacts through use of the filters (46% reduction in diarrheal disease in users versus non-users), a detailed analysis of economic and social factors that have contributed to success in some interventions and failures in others, identification of key challenges to scaling up the technology at the country level, and reliable estimates of field performance in reducing microbiological contaminants. This holistic approach is now being considered as the model for how best to assess point-of-use water treatment interventions worldwide.

Comprehensive study of long-term filter use and factors related to successful use

  • Key findings were:

  • Filters maintained effectiveness after up to nearly four years in use, both in terms of microbiological performance and impacts on user health.

  • Filters were susceptible to breakage, which was the primary cause of discontinued use. Maternal education, household investment in the technology, and other key factors were determined to be associated with effective long-term use of ceramic filters. NGOs conducting interventions now have evidence that selling the filters results in longer duration of filter use, and that education and both technical and moral support provided to user households can contribute to long-term effectiveness.

  • The filters were associated with an estimated mean 46% reduction in diarrhea in filter users versus non users (LPR 0.54, 95% CI: 0.41-0.71; 0.52, 95% CI: 0.32-0.86 in under 5s), powerful evidence that the filters are having a significant impact on public health.

Water quality impacts: E. coli, turbidity

Prospective cohort study to determine overall health impact


To meet our objectives, this study was carried out in three parts: (i), a cross-sectional study of the 2000 households that originally received filters to determine uptake and sustained long-term use, as well as factors associated with continued use or disuse of the technology; (ii), a water quality assessment in 80 households successfully using the filters (from part i) to determine the microbiological effectiveness of the filters in treating household water, focusing on both treated and untreated water; and (iii), a longitudinal health study comparing diarrheal disease prevalence in 80 households using the filters successfully to 80 control households (without filters).

Users and matched controls were interviewed to determine longitudinal prevalence of diarrheal diseases and other health outcomes.

  • Access to new and replacement parts and filters was limited in the study areas, because supply chains were not well developed. We found evidence for strong and growing demand for the filters: critical information for scaling up coverage.

  • Filters were susceptible to re-contamination under field use conditions, probably because users were "cleaning" filters and their associated water storage vessels with soiled rags. This had not been observed before; NGOs implementing the filters now incorporate training in hygienic filter cleaning to specifically address this issue.


An emerging household-scale water treatment technology is the ceramic water purifier (CWP), a household-scale, porous ceramic filter adapted locally from the Potters for Peace model developed in Central America. This study included filters produced by International Development Enterprises (IDE) from 2002 and Resource Development International (RDI) from 2003. Filters are produced by molding clay mixed with ground rice husks, firing in a masonry kiln, and treatment with a silver-based microbiocidal solution to protect against recontamination in use. For more information on similar ceramic filters around the world, visit www.pottersforpeace.org.

This trial spanned three provinces and thirteen rural villages in Cambodia.

User support and training is critical to long-term use and effectiveness of the technology.

  • The filters reduced E. coli by a mean 98% under long-term, daily household use conditions. This was lower than expected, because laboratory results had indicated 99% - 99.99% reduction in bacterial pathogens. We now know that user behavior and filter care practices can adversely impact filter effectiveness, and that these factors are critical to the maintenance of a high level of performance in reducing microbes.

  • Microbiological effectiveness of the filters was not observed to be closely related to time in use, indicating that filters maintain their effectiveness over long periods of time. Based on this finding, NGO recommendations that users replace the ceramic filter elements every one or two years (as was standard practice) may not be necessary.

Access to filters and filter unit parts is difficult for rural users, who may live in remote areas with seasonally impassable roads.

Interviews with 506 households yielded a robust data set for analysis.

Factors associated with uptake and long-term use of the filters in Cambodia.

The filters included in this project were distributed by NGOs with varying levels of cost recovery using a number of different implementation models both with and without user support, education, and training.

CWP production in Cambodia is now evolving from a subsidized, NGO-based endeavor to market-based, full cost recovery schemes that are intended to boost sustainability and coverage. The filters now retail for US$7.50-$9.50 per system (and US$2.50 - $4.00 for replacement filters). Cost estimates per liter of treated water range from US$0.00025 to US$0.001. Some filters are still distributed at subsidized prices to the poorest households.


Control households in the prospective cohort study received new filters as part of their participation in the study. User support and training is essential for uptake and long-term, consistent use of the technology. NGOs in Cambodia are incorporating lessons learned from this study in scaling up access to ceramic filters across Cambodia.

We thank Uon Virak, Choun Bunnara, Lim Kimly, Michelle Molina, Oum Sopharo, Song Kimsrong, and Van Sokheng for conducting interviews and analyzing water samples. Special thanks to project manager Sorya Proum. Thanks also to Jan-Willem Rosenboom of the Water and Sanitation Programme, the Cambodian Ministry of Rural Development, and Douglas Wait and the UNC Environmental Microbiology and Health group. This project was commissioned by UNICEF and WSP-World Bank. The views expressed in this poster are the views of the authors and do not necessarily reflect the views or policies of the United Nations Children's Fund or the Water and Sanitation Programme.

Microbiological testing of pre- and post-treatment water yielded key data on long-term filter effectiveness under field use conditions.

Filter being cleaned: unsafe practices while cleaning can lead to reduced effectiveness.