Flow cytometry

Flow cytometry in drinking water practice

The microbiology of drinking water has two main aspects: hygienic and general quality. The hygienic quality is related to the pathogens that are spread by fecal-oral route, and the overall quality is related to native microbial communities in water treatment and distribution systems.

Indigenous microbial communities play an important role in the production of healthy drinking water. A deviation indicates a disruption in its purification or distribution process, for example due to intrusion of contaminated water, dysfunctionalities in treatment processes, deviations in chemical water quality, regrowth, and biofilm formation.

Native microbial communities have traditionally been monitored with the bacterial count that provides information about the number of heterotrophic bacteria capable of growing on a non-selective nutrient medium. However, counting the colony number is no longer the best available technology in terms of relevance, simplicity, reliability, and speed.

The promising alternative to this, is Flow Cytometry. New techniques, including flow cytometry, show that the amount of bacteria in water is much higher, and that bacterial communities are much more complex than previously thought. The drinking water microbiome can contain as many as 9,000 different taxa, with a total bacteria number of 1,000 - 500,000 per milliliter. With flow cytometry, quick and accurate (virtual) counting of all bacteria in a water sample can be achieved.

Since 2010, Het Waterlaboratorium has been carrying out flow cytometry analyses for drinking water companies. In 2020, a Dutch-Flemish platform, chaired by Het Waterlaboratorium, was launched. The aim is to standardize the application of flow cytometry in drinking water practice for the routine monitoring of general microbiological water quality, from source to tap.