Budapest’s Tap Water Remains High-Quality for a Long Time to Come

Although International Danube Day was celebrated on 29 June, our responsibilities extend beyond that single day; there are challenges to address every day. This is underscored by the recently published findings of the consortium researching the waters of the Danube. The research team included the HUN-REN Centre for Ecological Research, Budapest Waterworks Ltd., the National Public Health Centre, the Budapest University of Technology and Economics, and the University of Miskolc.

The five-year project began with an intensive sampling programme, during which samples were taken every two weeks for a year from the Danube, groundwater, wells, process points, and the distribution network. The system was monitored under a wide range of hydrological and climatic conditions, including periods of very low water levels in the Danube and instances of pollution. The results are reassuring.

"Using models based on the measurement results, we can predict what to expect in the coming years and decades, in terms of the vulnerability of the Danube's water filtration system and its ability to provide the safe drinking water we enjoy today," Attila Engloner, ecologist and project leader, told HUN-REN.

The Danube’s natural filter works well

Water from the Danube is filtered through a gravel bed lining the riverbed, where microbial communities on the surface of the gravel form a biofilm layer. As the water passes through this layer, its quality is significantly improved, making the water from the production wells along the Danube virtually potable. In addition, water utilities further treat the water (primarily through chlorination) as it travels long distances through distribution networks before reaching our taps. For safe drinking water, it is essential that the water remains as safe at the end of its journey as it was when it left the waterworks.

According to Attila Engloner, the project's most important finding was that this system effectively filters out a significant portion of the potentially harmful substances they examined, even under extreme conditions such as massive flooding or very low water levels. He added that the river's flow rate, i.e., the volume of water transported is also a crucial factor, as there are over 700 drinking water production wells in Budapest, primarily concentrated in two main areas: to the north on Szentendre Island and to the south on Csepel Island. The distance and depth of these wells vary. Nevertheless, the results of the five-year research indicate that there will be no threat to the quantity or quality of Budapest's drinking water production in the next 20 to 30 years.

The research also examined the sediment suspended in the Danube, which can obstruct the pathways where water seeps into the sub-riverbed layers. These investigations yielded reassuring results, indicating that this sedimentation is not expected to significantly impede subsurface infiltration or the functioning of the bank filtration systems.

There are hazardous substances in the Danube, but they currently do not pose a problem for drinking water

Water quality was examined from both chemical and biological perspectives. Chemical substances can be categorised into traditional pollutants and new types of pollutants. Traditional pollutants have been known for a long time and have a more extensive research history (such as forms of phosphorus and nitrogen, as well as heavy metals). The emergence of new types of pollutants is more recent, and we know less about them; examples include pharmaceutical residues and microplastics. (The latter were not included in the research.)

"With new types of pollutants, we often do not yet know precisely what effects they have, how they break down, and what their degradation products cause," said the project leader. The study examining the water of the Danube analysed 41 different organic micropollutants, including substances such as antihypertensives, anti-inflammatories, contrast agents, and pesticides. Although 31 of the 41 molecules are found in the Danube, they are fortunately present in very low concentrations, posing no public health risk (they occur at levels well below health threshold values). Engloner also provided an example: based on a daily water consumption of 2 litres, it would take 22,000 years to consume the equivalent of one tablet of the antihypertensive drug Telmisartan through drinking water.

However, it is not only water quality that can be affected by pollutants, but also the ecosystems of the Danube (similar studies have recently been conducted at Lake Balaton, which we covered in more detail here). According to the project leader, prevention is the most important aspect; we should not thoughtlessly pour everything down the drains, as we do not know how many substances behave in natural waters.

September is already considered a summer month for the Danube

The microbial community in the waters of Hungary's largest river is influenced not only by sudden, large floods and prolonged low flows but also by temperature, particularly as a result of climate change. Research has shown that the Danube still retains its summer microbial composition in September, and this warm period is increasingly extending.

Water consumption is influenced by us, the everyday users, and can even lead to temporary or localised water shortages. “We need to think carefully about how we use our water, not only for domestic consumption but also in industry,” said Attila Engloner. According to the project leader, the nature of water demand is also important when discussing the long-term security of drinking water or water supply. “It makes a difference whether water demand is high in summer or winter, and in which geographical area. We need to make responsible decisions about how, for what purposes, and how much water we want to use in the coming decades,” he emphasised.

About the project

Building on the National Water Research Programme of the Hungarian Academy of Sciences, the "Clean drinking water: multidisciplinary assessment of secure supply from the source to the consumers" project assessed the risk factors affecting the safety of water resources and drinking water from water abstraction to the point of consumption—in other words, from the Danube catchment to the tap. The project was funded by the National Research, Development and Innovation Office within the framework of the National Excellence Programme, with a total budget of HUF 1,040,189,000.