What Makes an Efficient Ceramic Water Filter?

An important but brief study was published last year by individuals working with the RDIC factory in Cambodia to find what factors make a more efficient ceramic water filter. In this study several empirical tests were preformed to investigate the relationships between filter mix ratios and firing schedules. Perhaps the most relevant results demonstrated by these tests demonstrated the lack of correlation between flow rate and bacterial removal efficiency. In the test, filter discs ranging from 2 to 18 liters per hour showed similar e-coli removal efficacy.

This has long been suspected in the industry where standard flow rate best practices specify a 1.5 to 3 liter range of acceptability. These flow rates were set in an attempt to ensure that new factories making filters were producing effective ceramic water filters without the ability to effectively test their real ability to remove bacteria.

Other Tendencies of Efficient Ceramic Water Filters

  • Increasing burnout to clay ratio seems to increase flow rate while reducing strength
  • Firing to a higher temperature may increase flow rates, (it is assumed that firing higher increases pore size)
  • Increasing firing temperature may result in a stronger filter.
  • Firing higher seemed to reduce bacterial removal effectively, but the correlation was weak.
  • There is strong variation in flow rates of filters formed in wet or dry season.
  • Similar flow rates can be achieved by 1: Increasing burnout to clay ratio and reducing burnout particle size 2: Reducing burnout to clay ratio and increasing burnout particle size.

This study clearly presents an argument for further testing of these same variables to produce a more efficient ceramic water filter.

The onus is now on each factory to further develop their manufacturing practices. If the established best practices are to be modified on a case by case basis it should only be by careful experimentation and with the partnership of an independent monitoring agency to ensure that filters being produced meet minimum bacterial removal standards.

Although these results direct us towards a path of study that develops efficient ceramic water filters, any operation in the manufacturing process which relies on additional mechanical or technological resources also removes a layer of appropriateness to the ceramic water filter technology as a whole.

Imagine, for instance, that to make a more effective filter we find that burnout must be screened to finer tolerance. The factory in Somalia must then find a new reliable source a new mesh for their screening machines. The mesh they are currently using comes from out of the country and is very expensive and difficult to obtain. I argue that although the finer mesh would result in a more effective filter, if the basic standards were to change to reflect the greater efficiency it would reduce the appropriateness of the technology as a whole.

Development of a more effective filter is a part of factory scalability, once production of a basic filter has been stabilized a factory is ready to begin the process of improvements. These improvements will be determined by the local environment. After all, there are plenty of more effective filters on the market when cost, manufacturing limitations, and community adaptability are removed from the qualifications.

Studies such as these are important for us to better understand the path ahead with regard to improvement/changes to ceramic water filter production practices. That said, many of the studies assessing these practices are conducted in research facilities using laboratory methods. While this is a necessary first step, it must be followed by a replication of the results in a working filter factory. If this was a part of all academic research there would be a lot less ambiguity.

Link to original study:
Isabelle Gensburger – October 2011

RDIC Ceramic Water Filter Manual

This is a first publication of RDIC‟s ceramic water filter production techniques, ideas and visions. We
are planning additions and amendments into the future. So stay tuned and keep in touch as we
continue to refine and provide further information to assist you with your factory projects. Information
on updates can be found at http://www.rdic.org


Use of Ceramic Water Filters in Cambodia

Ceramic filter pilot projects (2002-2006) in Cambodia have yielded promising results that suggest these
interventions can be effective in improving drinking water quality and can contribute to substantial
health gains in populations using them.

“Executive Summary
Household-scale ceramic filtration technology is considered among the most promising options for treating drinking water at the household level in developing countries (Lantagne 2001; Sobsey 2002; Roberts 2004). Its use is Cambodia is widespread and growing, with the involvement of local and international NGOs and government efforts that have been supported by UNICEF, WSP-Cambodia, and others. Although several different kinds of ceramic filters are used for household-scale water treatment worldwide, among the most widespread is that promoted by Potters for Peace, a US and Nicaragua-based NGO; the Cambodian version is known as the Ceramic Water Purifier (CWP). It has been used in Cambodia since its introduction in 2001. Based on early successes in Cambodia (Roberts 2004), further investment in the technology is planned by NGOs and the Cambodian government. Stakeholders identified evaluation of the CWP experience to date in the country as vital to inform the scale up process and to identify lessons learned in the first 4 years of production and implementation. Part of this evaluation was an independent study commissioned by UNICEF and WSP-Cambodia to critically examine two major implementation efforts to date in Cambodia undertaken by the two main producers, IDE and RDI. The goals of the study were to characterize the microbiological effectiveness and health impacts of the CWP in target populations, and to identify successes and potential challenges facing the scale-up and implementation of the technology. The results of the study and program recommendations are presented here.”


Effectiveness of Ceramic Filteration for Drinking Water Treatment in Cambodia

Joseph Mark Brown
A dissertation submitted to the faculty of the University of North Carolina at Chapel Hill
in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the
Department of Environmental Sciences and Engineering.

Chapel Hill 2007


(Under the direction of Mark D. Sobsey, Ph.D.)
For the estimated 66% of Cambodians without access to improved drinking water sources and the potentially much greater percentage without consistent access to microbiologically safe water, point-of-use water treatment coupled with appropriate storage to prevent recontamination is a promising option for securing access to safe drinking water. The ceramic water purifier (CWP) is an emerging point-of-use water treatment technology that is made locally in Cambodia and in several other developing countries based on a design originally developed in Latin America in the 1980s. Despite the filter’s increasingly widespread promotion and implementation as a public health intervention within Cambodia and worldwide, its effectiveness in reducing waterborne microbes and diarrheal disease in users has not been adequately characterized. This dissertation examines: (i) the microbiological effectiveness of locally produced ceramic filters in Cambodia against bacterial and viral surrogates in the laboratory and in field use; (ii) the health impacts of the CWP and a modified CWP in a randomized, controlled trial in a rural/peri-urban village; and (iii) the continued use, microbiological effectiveness, and sustained health impacts of the CWP after up to 44 months in household use in three provinces of Cambodia.


Ceramic silver impregnated pot filters for household drinking water treatment in developing countries

Master of Science Thesis in Civil Engineering
Sanitary Engineering Section
Department of Water Management
Faculty of Civil Engineering
Delft University of Technology
Doris van Halem
November 2006


The World Health Organization (WHO)/UNICEF assessed in 2000 that 1.1 billion people do not have access to ‘improved drinking-water sources’. Interventions in hygiene, sanitation and water supply make proven contributors to controlling this disease burden. The ambitious target established in the ‘Millennium Development Goal1’ (MDG # 7) is “halving the proportion of people without sustainable access to safe water and basic sanitation by 2015”. Providing
more than half a billion people with safe drinking water is a major task, especially because most of them are living in rural areas. Despite major efforts to deliver safe, piped, community water to the worldÂ’s population, the reality is that water supplies delivering safe water will not be available to these people on such a short term. According to the WHO a short-term solution to meet the basic need of safe drinking water can be found in household water treatment and safe storage (HWTS).