Checking drinking water quality: a new bacterial counting technique

Robert Koch founded modern bacterial drinking water quality control in 1883 with his description of a method for determining the cell count of microorganisms in soil, air and water. Ever since, bacterial count has served as a parameter for monitoring water quality and as a measure for checking the efficacy of drinking water purification. Alongside more recent, more specific methods, the heterotrophic plate count (HPC) is still determined today in almost exactly the same way and, in accordance with the established standard, is limited to 300 colonies per millilitre.

It is now known, however, that the actual bacteriological status of drinking water is not really comparable with bacterial growth on an artificial culture medium. The total number of bacteria present as determined using flow cytometry is typically up to 10,000 times higher than the figure determined using aerobic colony counts.

Flow cytometry measurement, which is based entirely on the number of organisms present in a sample of drinking water, provides a much better indication of water quality than is possible using traditional analytical techniques that detect only a fraction of the microorganisms present.