New microbiological parameters of the EU-DWD

Significance of the new microbiological parameters of the EU Drinking Water Directive for German water supplies

Sampling point near Cologne at the Rhine

In the EU Drinking Water Directive adopted in January 2021, an operational part was included as an important innovation in Annex II for raw water and treated water.

For raw water, "somatic coliphages" are required as a parameter for microbial risks. The way in which this requirement is implemented is left to the member states in their national implementation.

The aim of this DVGW research project is to conduct a microbial risk assessment through data evaluation and specific investigations for pathogens and indicators in various exemplary water works, covering the wide range of water treatment processes commonly used in Germany. This is meant to serve as a basis for a sensible and appropriate implementation of the microbiological requirements of the new EU Directive into national law.

In the new EU Drinking Water Directive (EU-DWD), a so-called "risk-based approach" was included, which provides, among other things, that the raw water and, if necessary, also the treated water should be tested for "somatic coliphages" as an operational parameter for recording the microbial risk, in particular from faecal viral pathogens.

The parameter "somatic coliphages" is used to verify the removal efficiency for small particles in the size range of viruses.

The presence of pathogens must be considered especially for water supplies using raw water from surface water or raw water influenced by surface water. These include the raw water types surface water, i.e. river, lake and reservoir water, and the raw water types with surface water influence, i.e. bank filtrate, enriched groundwater and spring water. According to the industry picture of the German water industry 2020, these raw water types account for a total of almost 40 % of water production in Germany.

For quantitative microbial risk assessment, a procedure for highly contaminated river waters was developed within the framework of the DVGW-project W201517 and 201808 (QMRA). This approach requires extensive measurements of pathogens and the determination of removal efficiency by bacterial and viral indicators. It was shown that a very effective removal efficiency of about 2 log is achieved by a short underground passage of 2-5 days, but that this does not allow to reach a health based target for these pathogens, especially not for the bacterial pathogen Campylobacter and the enteropathogenic viruses. There is no experience so far for water works using raw waters with longer-lasting underground passages that already show approximately the microbial quality of deep groundwaters on the basis of indicators. For the quantification of indicators in these waters the detection limit is already reached, therefore no exact calculation of the removal efficiency for the underground passage is possible.

Therefore, within the framework of this project, specific investigations for bacterial and viral pathogens will be carried out with cultural and PCR methods as well as for indicators at water works with varying degrees of surface water influence (direct treatment, short bank filtration, artificial groundwater recharge, long bank filtration). The focus is on the pathogens Campylobacter (bacterial) and enteropathogenic viruses (Adeno-, Entero-, Noroviruses) identified as particularly relevant in the preceeding QMRA-project. In addition, the historic data of the microbiological indicators of the surface waters and raw waters already available at the water works will be compiled and evaluated after the first treatment steps. Depending on the expected concentrations, also innovative enrichment methods will be used, in order to enable the detection of pathogens and indicators.

With these new data, a microbial risk assessment should be reached with regard to the potential presence of pathogens and as such a basis for a sensible and appropriate implementation of the microbiological requirements of the new EU Directive into national law is to be created.