The distribution of drinking water without chlorine is the calling card of the Dutch water utilities. What makes it possible is the exceptionally high quality of the drinking water produced in the country. Microbially safe drinking water is a precondition for good public health. The presence of pathogenic microorganisms, even at concentrations under the measurement limits, can represent an unacceptable risk for public health. Water utilities therefore make use of several barriers in their surface water treatment processes. A closely considered selection of such barriers is needed to avoid unnecessary costs and environmental impact.
Since 2001 the water utilities have been required to conduct an analysis of microbial safety of drinking water (Dutch initials: AMVD) to demonstrate that their drinking water satisfies the legal threshold values for the infection risk of 1 infection per 10,000 people per year. The current AMVD Inspection Guideline is now being reviewed to transform it into the AMVD Guide. This is being done within the Infection Risk Working Group (WIR). The experience of the water utilities and the results of international scientific research in the field of quantitative microbial risk assessment (QMRA) are to be incorporated in the new Guide. This project will contribute to this process, as well as unlock or develop the knowledge required for the implementation of the AMVD. By exploring, developing and applying new insights, the most up-to-date knowledge is being activated to secure microbially safe drinking water. All the steps in the QMRA and AMVD process are described below, together with the related contributions of this project.
Gathering all knowledge about pathogens and treatment
The AMVD focuses on ‘index’ pathogens, which are selected on the basis of their occurrence in drinking water sources, behaviour during treatment and impact on public health. A database with information about the occurrence and the dynamic of pathogens and indicator organisms in water and contamination sources will be developed. This can be used to develop sampling programmes for new situations, as well as to test sampling programmes. The ratio between indicator organisms and pathogens in different situations also provides a basis for risk assessment in the event of the (unexpected) detection of indicator organisms in various situations. The database will be unlocked via a web-based tool.
From 2014 to 2016, the framework for the AMVD Reference Document was developed on the basis of Operational Guidelines, with protocols/tools for the collection, documentation, analysis and presentation of literature data on the effectiveness of water treatment. In the new AMVD Guide references will be made to this AMVD Reference Document. In BTO 2018-2023 this path will be pursued further with the ultimate goal of encompassing all treatment processes. The databases and web-based tools are being created per process in this BTO project, and thus offer a framework for the literature data. The literature studies for the different processes will be carried out in various projects, for example in a partnership with the University of Colorado in Boulder. Due to budgetary constraints they will not, however, be carried out within this project, but rather on an ad hoc basis in other research projects.
Alternative virus indicators of treatment effectiveness
The Exploratory Research showed that, by making use of the new possibilities offered by molecular methods, natural viruses can be used to research the removal of viruses by drinking water treatment processes in practice. In this way, it is possible, without using concentration methods, to show removals of more than 7 log, which is far higher than can be achieved with today’s indicator viruses. The method should therefore also be applicable to determine high log removals by treatment technologies and soil passage (river-bank filtration, dune filtration). The method will be more extensively tested at more sites to determine whether these alternative viruses occur in sufficient numbers. If this proves to be the case, the removal of the alternative viruses will be compared with that of human viruses (noro-, adeno-, enterovirus).
Model for faecal contamination in dune passage and limestone abstraction
Soil passage provides an important pathogen barrier for a number of water utilities. In fragile phreatic groundwater abstraction, the unsaturated zone forms a barrier against pathogens from the surface. A number of water utilities use dune passage to treat their drinking water. These infiltrating systems are very effective in the removal of faecal pathogens and the indicator bacteria E. coli and Enterococci are in principle absent in the abstracted water. Sometimes however E. coli are found in the extracted dune filtrate or the groundwater. This is probably a result of the migration of E. coli bacteria from the surface. Such migration in these situations occurs notably during heavy rainfall, if faeces are present on the surface near the abstraction operations. In 2012, a model was set up to calculate the risks for dune passage of the migration of pathogens. Since then research has been conducted in several areas, the results of which allowed the model to be added to and improved. Within this project the latest results from the international literature and KWR research will be incorporated in the model.
Review of AMVD guideline
The current AMVD Inspection Guideline is being reviewed, under the supervision of the Infection Risk Working Group (WIR), to produce the AMVD Guide. The results of the BTO research are being incorporated in the WIR, and will lead to an AMVD approach that is in harmony with the interest of the water utilities, namely, that of supplying affordable, safe drinking water with limited environmental impact. Besides participating in the WIR, KWR and RIVM will elaborate the proposed modifications and test them against data from practice.