HPC also frequently inhabit the inner regions of water filtration equipment. They can grow in carbon beds, for example, and they may be found in reverse osmosis units downstream of the initial dechlorinating filter. Although they may be a bit of an aesthetic nuisance, forming a slickness on the surface of filter cartridges, for example, they pose no threat to health.

"Although monitored by health officials, the presence of heterotrophic bacteria in public water supplies is seldom considered a public health threat."--Encyclopedia.com.

In one study of HPC in reverse osmosis units, the authors concluded:

Conversely, there may be benefits to higher levels of heterotrophic bacteria in drinking water. Rollinger and Dott present coincidental evidence that heterotrophic bacteria suppresses growth of coliforms and other enteric pathogens (7). In another study, inoculation of filters with three different pathogens resulted in no vigorous growth, and even an eventual die- off when dechlorinated tap water was being filtered (8). Thus, some evidence indicated there may be benefits to having heterotrophic bacteria populate filters.To read the full article.