48 of the samples collected from collaborating water company distribution systems and tested using standard methods were also tested using flow cytometry . Total cell count results obtained reflect typical concentrations observed in previous studies on drinking water , in the order of 10 4 to 10 5 per ml of diverse microbial populations ( Hoefel et al . , 2003 ) . Comparison of the portable device peak T intensity and these flow cytometry data , Fig . 5 , reveal a reasonable correlation ( r 2 = 0.56 ) and certainly an improvement in comparison to the regulatory microbial measures . It is interesting to note that the error bars associated with technical repeats of flow cytometry are generally greater than those associated with the new fluorescence device . The improved correlation reflects the benefits of flow cytometry identifying all bacteria in a sample rather than the culturable bacteria only . Hoefel et al . ( 2003 ) demonstrated that HPC counts in a mix of raw and potable waters were generally 2 - 4 log fold less than the numbers of total bacteria reported using the same stains as the BacLight ™ Kit in this study . With peak T fluorescence capable of picking up an area of identifiable bacterial activity , a correlation would therefore be anticipated .