Assessment of occurrence of somatic coliphages in drinking water in Poland

The use of Escherichia coli and enterococci as indicators of the presence of pathogenic viruses or parasitic protozoa is limited. In order to increase the control of enteric pathogens in drinking water, Directive (EU) 2020/2184 of the European Parliament and of the Council incorporates into microbiological analysis the determination of somatic coliphages as a new operational parameter in raw water for controlling the effectiveness of treatment processes. The goal was to assess the occurrence of somatic coliphages in raw water samples collected at groundwater and surface water intakes, and in treated water samples fed into the distribution system.

The study included 7 groundwater intakes and 6 surface water intakes at Water Treatment Stations. A total of 52 raw water samples and 40 treated water samples were assessed. Somatic coliphages were determined according to PN-EN ISO 10705-2 and PN-EN ISO 10705-3 (with modifications).

The results showed the presence of somatic coliphages in low numbers in 8% of water samples collected at groundwater intakes and in 89 % of samples collected at surface intakes. In 44 % of the water samples tested, the number of somatic coliphages was higher than 50 pfu/100 ml. Somatic coliphages were not detected in any of the treated water samples.

Somatic coliphages can be a useful operational monitoring parameter and a tool for strengthening the control of waterborne pathogens in assessing the effectiveness of water treatment processes. The implementation of somatic coliphage determination for water intakes where there is a risk associated with faecal contamination, should be part of ensuring adequate drinking water quality.