The role of colony count in water supply

Tuesday, July 1, 2014

Autors: Beatrix Párkány-Simon, Dr. Anikó Brumbauer


Drinking water is one of the most strictly controlled foods, characterized by the fact that its chemical and physical properties are by and large stable, but it is a biologically active medium, which is controlled by water companies using disinfection. In addition to bacteria indicating fecal contamination, so-called indicator organisms, such as colony counts, also play an important role in checking the efficiency of the treatment. Colony counts used for the general microbiological characterization of waters are the number of colonies of bacteria culturable at 22 and 37 oC, and their testing according to the standard provides the operator with quantitative information about general bacteriological contamination. Our goal was to identify microorganisms occurring in the production and service areas of the Waterworks of Budapest, and also their resistance to chlorine-basaed disinfectants. Based on our results, the bacteria identified are biofilm-forming organisms not harmful to health that commonly occur in aqueous systems. However, in case of strains isolated from production areas, efficient disinfection was only achieved by using chlorine concentrations several tens of times higher than that applied during chlorination of the supply network.

2. Introduction and literature overview


Chemical characteristics of drinking water are determined mainly by the water source, and they can be kept stable by choosing a suitable water treatment technology. However, drinking water is not a sterile medium, so it might contain bacteria and their presence is influenced by the water source, the water treatment process, disinfection, the condition of the network and certain physical factors [1]. Microbiological testing of drinking water extends to bacteria indicating fecal contamination and to so-called indicator parameters [2]. The latter include, as cumulative parameters, bacteria that can be cultured at 22 and 37 oC, which provide quantitative information about microorganisms present in the water. They provide useful information to the characterization and supervision of drinking water, such as evaluation of the efficiency of water treatment procedures, monitoring of the condition of water distribution systems or forecasting serious contaminations. The major benefit of colony counts lies in observing changes relative to expected values, based on long-term observations [3].

Colony counts larger than usual values indicates increased microbiological activity in drinking water, which can be caused by the following reasons or factors [4]:


·      increased amount of energy and carbon sources in water (organic matter content);

·      contaminated/infected materials or equipment in contact with drinking water;

·      presence of sediments;

·      change (increase) in water temperature;

·      changes in hydraulic conditions (flow rate), possible development of turbulence;

·      presence/absence of disinfectant, mechanism of action of disinfectant;

·      residence time longer than allowed in the technology (stagnant water).

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