Source water quality is a key determinant of drinking water quality. The recast European Union 2020/2184 Drinking Water Directive (DWD) introduced the obligation for comprehensive risk assessment in drinking water supplies, including hazard assessment of the water source. The DWD also requires further elements of natural origin to be monitored, including U, Ca, Mg and K. The current study is the first comprehensive assessment of 15 natural elements (B, Ba, Be, Ca, Co, K, Li, Mg, Mo, Na, Se, Sr, Ti, U and V) in 1155 (82%) Hungarian drinking water sources, including surface water, bank filtered and groundwater sources. Parameters posing a risk to health (Se, V and U) were typically below the limit of quantification (LOQ), but higher concentrations (max. 7.0, 17 and 41 µg/L, respectively) may occur in confined locations. U exceeded the DWD parametric value in one water supply. Mg and Ca in the majority of the water supplies and Li in a small geographic area reached the concentration range assumed to be protective to health. Water sources were grouped in six clusters based on their elemental distribution, some of them also showing clear geographical patterns. Surface and groundwater sources were not differentiated by composition, with the exception of karstic waters (dominated by Ca and Mg). None of the investigated parameters are expected to be a source of public health concern on a national level, but local occurrences of U and Se should be investigated and managed on a case-by-case basis.

Source water quality is a key determinant of drinking water quality. The recast European Union 2020/2184 drinking water directive (DWD) introduced the obligation for comprehensive risk assessment in drinking water supplies, including the water source and incorporated new elements of natural origin in the list of parameters to be monitored. The current study is the first comprehensive assessment of 15 natural elements (B, Ba, Be, Ca, Co, K, Li, Mg, Mo, Na, Se, Sr, Ti, U and V) in 1155 (82%) Hungarian drinking water sources, including surface water, bank filtered and groundwater sources. Parameters posing a risk to health (Se, V and U) were typically below the lower limit of quantification (LOQ), but higher concentrations (max. 7.0, 17 and 41 µg/L, respectively) may occur in confined locations, the latter exceeding the DWD parametric value in one water supply. Li in a small geographical area, Mg and Ca in the majority of the water supplies reached the concentration range assumed to be protective to health. Water sources were grouped in 6 clusters based on their element distribution, some of them also showing clear geographical patterns. Water types were not differentiated, with the exception of karstic waters (dominated by Ca and Mg). None of the investigated parameters are expected to be a source of public health concern.

Lead remains a public health priority, in spite of long-standing mitigation efforts. In drinking water, the source of lead is primarily the domestic distribution system. Thus, regulatory compliance monitoring fails to capture the magnitude of the problem. In order to assess lead concentrations in drinking water and identify populations at risk of lead exposure via drinking water, a nationally representative survey was carried out in Hungary. Municipalities were categorized and, where necessary, subdivided into neighborhoods based on the type of municipality, the corrosive nature of the supplied drinking water, and the potential presence of lead pipes in the mains and the domestic distribution systems. A total of 58 representative residential areas were selected for a 6-month sampling campaign. Random daytime (RDT) and 1 min flushed samples were collected from residential and public buildings and analyzed for lead by inductively coupled plasma mass spectrometry. Non-compliance rates were significantly higher in buildings built before 1945 (25% compared to 7% in newer buildings), when the use of lead pipes was general practice. Flushing reduced lead levels significantly, corresponding to 14% and 6% non-compliance in the RDT and flushed samples, respectively. No association was found with corrosive versus protective water quality. High risk areas were primarily identified in the capital and historic centers of cities. The results were translated into public information tools including a searchable map of lead risk areas and a simplified risk assessment tool for consumers. The survey outcomes also support national risk assessment for lead in drinking water, an upcoming obligation under the recast European Union drinking water regulation.

Riverbank-filtered systems are cost-effective and sustainable drinking water supply systems along major rivers. However, they are strongly dependent on the river stage. Climate change-induced extremely low or high river stages may cause water quantity and quality problems. In this study, a riverbank-filtered drinking water supply system along the Danube River in Hungary was investigated from a geochemical aspect at lower and higher river stages. We also aimed to understand the origin of elevated (>100 mBq L–1) gross alpha activity measured in some wells. 10 producing, 2 monitoring wells, and the Danube were sampled at lower and higher river stages. Physico-chemical parameters were recorded on-site and the samples were analysed for major ions, trace components and hydrogen (δ2H) and oxygen (δ18O) stable isotopic compositions as well. 234U, 238U and 226Ra activity concentrations were determined by alpha spectrometry using selectively adsorbing Nucfilm discs. 222Rn activity was measured by liquid scintillation counting. Uranium activity was measured in the highest concentration (up to 222 mBq L–1) among the examined radionuclides. 226Ra and 222Rn activities were barely above the detection limit. Based on these results, the previous non-compliant elevated gross alpha activity is caused by dissolved uranium in the groundwater. A spatial pattern was recognized in the geochemical characteristics of the produced water. Total dissolved solid, iron and manganese content and also uranium activity concentrations show increasing values from N to S, which corresponds well to the occurrence of organic matter-rich, clayey floodplain deposits underlying the aquifer and to their higher position to the S. Stable isotope ratios point to the increased influence of surface waters in the N due to the position of an irrigation channel. Besides spatial variation, a temporal change was observed, too: higher uranium activity was measured at a lower river stage (up to 222 mBq L–1) compared to concentrations at a higher river stage (up to 126 mBq L–1). This phenomenon could be explained by the dynamic relationship between the groundwater and the river. The hydraulic gradient between the river and the wells decreases with decreasing river stage, which resulted in longer residence time of the water. The longer the residence time, the more the oxygen-rich water interacts with the clayey basement layers facilitating uranium remobilization. This process will become increasingly dominant in extremely low river stages during long-lasting drought periods in the future and might lead to water quality problems. Our study highlights the vulnerability of riverbank-filtered drinking water supply systems, which can jeopardize their long-term use in the future. The research is part of a project which was funded by the National Multidisciplinary Laboratory for Climate Change, RRF-2.3.1-21-2022-00014.