Relationships between levels of heterotrophic bacteria and water quality parameters in a drinking water distribution system

Conventional plating methods were used to quantify heterotrophic bacteria from a drinking water distribution system. Three media, plate count agar (PCA), R2A agar and sheep blood agar (TSA-SB) were used to determine heterotrophic plate count (HPC) levels. Grab samples were collected weekly during the summer and autumn of 1997 at four locations in a municipal water distribution system. The four sampling sites included the water treatment plant, a vertical standpipe, a booster pump station and a private residence along a dead-end mainline. The pump station and private residence were also instrumented with water quality probes and on-line bioreactors. Relationships between levels of HPC bacteria and standard physical and chemical parameters were examined. HPC levels from R2A agar were found to be uncorrelated with HPC levels on TSA-SB agar at all four locations. Orange and yellow pigmented bacteria were the dominant expressions in all bulk fluid and biofilm samples. The fraction of pigmented bacteria in bulk fluid samples was greatest at the standpipe. Pigmentation percentages were found to be uncorrelated with standard physical and chemical parameters of water quality in distribution systems.