- Heterotrophic Bacteria. How much a threat?

"A new battle is raging in government and scientific circles regarding the health effects of heterotrophic bacteria. The fight could affect every water treatment dealer in the United States. Heterotrophic microorganisms, single-celled creatures that may cause gastrointestinal illness and pneumonia in some people, multiply in point-of-use/point-of-entry (POU/POE) equipment. Granular activated carbon (GAC) filters, the most popular form of filtration, creates an ideal home for these bacteria..While most heterotrophic bacteria are harmless, mounting evidence shows that some members of this microscopic family are a health threat. The problem for water treatment dealers is that their equipment may be exacerbating the contamination. Heterotrophic micro-organisms similarly grow in on-the-shelf bottled water, well water pressure tanks, and in water in household plumbing. ...If heterotrophic bacteria are dangerous, federal and state regulators might require dealers to install additional treatement devices, such as ultraviolet or reverse osmosis (RO) systems, to prevent bacterial proliferation....'Heterotrophic bacteria clearly do pose a danger, the degree of which is poorly characterized', says National Drinking Water Advisory Council member, Dr. Jeffrey K. Griffiths, associate director, Graduate Programs of Public Health, Tufts University School of Medicine, Boston, Massachusetts....The EPA uses an informal standard of 500 colony forming units (CFU) of heterotrophic bacteria per milliliter to measure water quality and turbidity. The EPA standard is five times less strict than European standards, but high enough to fail most water treatment devices. A typical carbon filter that sits overnight contains between 1,000 to 10,000 CFUs.... A European study found that gram-negative bacteria in drinking water undergoing softening treatment. The study says softening treatment led to a 15-fold increase in heterotrophic counts and a 30-fold increase in gram negative bacteria, which include the pathogens pseudomonas and aeromonas [causing meningitis, pneumonia, septicemia and severe diarrhea- byline article]....Bacterial contamination of POU/POE [Point-of-use/Point-of-entry] treatment devices occurs because municipal water plants remove most bacteria but do not produce sterile water. Once a carbon filter removes chlorine, bacteria can multiply."

James Denn (Executive Director) in Heterotrophic menace: fact of fiction? in Water Technology, February 1999.