Assessment of Flow Rate as a Quality Control Test for Ceramic Pot Filters

The ceramic pot filter (CPF) is a low-cost household drinking water treatment system designed to provide potable water to families in developing countries. Among the indirect tests used for quality control the most common is the flow rate test, normally conducted with a T-piece tool. The target flow rate of a production sized CPF is 1 to 2 L/h, but the strength and type of relationship between flow rate and microbiological efficacy is not clear. The objective of this preliminary research was to understand how accurately current indirect testing procedures represent microbiological removal capacity. Fifteen experimental sized CPFs with different clay-burnout material ratios were made using methods and materials which mimicked CPF production at a filter factory in Guatemala. The experimental CPFs were tested to determine porosity, flow rate, and efficacy as measured by the logarithmic reduction value of total coliforms. Testing for the three parameters was repeated in Guatemala using six production sized filters from the local CPF factory. Collected data were studied to find relationships between the three parameters. Flow rates measured by the factory workers using the T-piece tool were compared with those determined in the factory laboratory. The results show that a linear or inverse relationship between efficacy and flow rate should be considered. The percent difference between flow rate measurements recorded using the T-piece tool and those conducted in the laboratory ranged from 1 to 45 percent. Further studies should be conducted with a larger sample of production sized CPFs to confirm the type of relationship and the commonly used range of 1 to 2 L/h