<br/>Point-of-use filters are often installed at sinks and fountains for a variety of reasons including lead or metals removal and for taste and odor removal. Experimental results showed filtered water is subjected to substantial biofilm formation which directly led to more bacteria presence compared to unfiltered water. In order to explore the cause of this filter effect on the drinking water quality, systematic statistical studies were carried out on water samples collected between 2011 and 2015 from 525 points of use either with or without filter installation in the DC area. About 29 water quality parameters (e.g. heterotrophic plate count (HPC), total chlorine, pH, ammonia, nitrite, temperature, alkalinity, total hardness, iron, orthophosphate, sulfate, UV-254, etc.) were analyzed from each sample. HPC was used as a main indicator of bacterial regrowth. Three statistical approaches, namely Principal Components Analysis (PCA), Multiple Linear Regression and Measures of Association were exploited as statistical tools to analyze the correlation between HPC and other water quality parameters. PCA test revealed that there are strong correlations of HPC values to total chlorine, pH and temperature, respectively. Measures of Association and Multiple Linear Regression confirm that low total chlorine and high temperature values tend to result in high HPC values. Between all water quality parameters analyzed in this study, it is the total chlorine that presents the highest correlation with HPC. Consistently, it was observed in our experiment that all filtered water tends to possess lower total chlorine but higher HPC values than unfiltered water. Since the filters simultaneously remove chlorine in addition to other contaminants, the lower chlorine together with higher temperature made filters a more suitable place for bacterial growth. This is especially true when filters are saturated with organic matters providing sufficient food source for bacteria to grow. Further studies should be conducted on how to balance the removal of metals, such as lead, and the resulting biological growth on the filters in building plumbing systems.

Statistical exploration of the cause of bacterial regrowth in filtered drinking water

254th National Meeting (2017)

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