Arsenic Speciation and Pressure Monitoring in a Hungarian Water Distribution Network

Arsenic concentrations in the groundwater in the Hungarian Great Plain region are naturally high with background levels up to 225 μg/L. Being largely dependent on this arsenic-rich water, Hungary has suffered compromised drinking water quality for decades. In 2016, the European Commission issued an infringement notice calling for compliance with the European Union Drinking Water Directive arsenic regulations for 66 non-compliant zones out of the 365 water supply zones in Hungary. As of 2022, the number of zones in non-compliance was reduced to 13 through the Environment and Energy Operative Program. Despite reforms, drinking water systems in Hungary are still susceptible to arsenic contamination due to accumulation and infiltration in the water distribution system. Trace amounts of arsenic not removed in water treatment processes can accumulate in biofilms, mineral deposits, and pipe scale within the distribution system. These arsenic-laden masses may release concentrated arsenic deposits when disturbed by pressure alterations triggered by repair and maintenance activities, power interruptions, and valve operations in the system. Arsenic-rich groundwater also enters the potable water supply during negative pressure events through pipe breakage and leaks in the pipe network. These pathways for arsenic exposure have not been thoroughly investigated and subsequent impacts to drinking water, especially in aging distribution systems and under increasing climate stressors, is uncertain.

Arsenic exposure was investigated in a small water distribution system in the Hungarian Great Plain because small systems are susceptible to high water age and low flows which can exacerbate contaminant buildup in the system. Weekly water samples from public faucets and source water were analyzed for temporal and spatial fluctuations in arsenic, manganese, iron, pH, conductivity, alkalinity, and oxidation/reduction potential from September 2024 to May 2025, with a 3-month break for winter. Total samples collected will be around 300. Nine fire hydrant-mounted pressure sensors were used with a hydraulic model to investigate hydraulic influences on water quality, while rainfall and water temperature were recorded to account for climatic factors. Water system maintenance activities were noted to account for external interference in normal system operations. Localized spikes in arsenic up to 14 μg/L were detected. The highest arsenic concentration was concurrent with maintenance activity, atypically high redox potential, and pressure drops in the system. Trend analysis and predictive modeling results will be presented to describe the relationships between hydraulic, climatic, and water quality parameters in the system.