Effective identification and quantification of groundwater (GW) infiltration into sewage collection networks represents an important step towards sustainable urban water management. In many countries, including northern regions, sewage networks are aging to the point where renovation is needed. This study focused on the utilization of stable water isotopes as tracer substances for GW infiltration detection. The main objectives were to investigate the validity of the method for quantifying GW infiltration in cold climate conditions and to test the robustness of this method under assumed low GW infiltration rates. In general, the stable water isotopes (δ¹⁸O) produced reliable results regarding origin identification and quantification of GW infiltration rates in winter conditions (continuous below zero temperatures and snow accumulation during preceding months). The 1.6‰ distinction between the δ¹⁸O isotope composition signals of the two water sources (drinking water from river and groundwater) in the studied network was sufficient to allow source separation. However, a larger distinction would reduce the uncertainties connected to GW-fraction identification in situations where low GW infiltration rates (<8%) are expected. Due to the climate conditions (no surface water inflow), GW infiltration to the network branch monitored represented the totality of I/I (infiltration/surface inflow) flows and was estimated to reach a maximum daily rate of 6.5%. This being substantially lower than the 29% yearly average I/I rate of ca 29% reported for the city's network. Overall, our study tested the stable water isotope method for GW infiltration detection in sewage networks successfully and proved the suitability of this method for network assessment in cold climate conditions. Isotope sampling could be part of frequent monitoring campaigns revealing potential infiltration and, consequently, the need for renovation.

The widespread presence of antibiotics in wastewater treatment plants (WWTPs) and receiving water bodies has emerged as a critical environmental and public health concern, primarily due to their persistence, ecological effects, and role in the development of antimicrobial resistance (AMR). This review synthesizes quantitative data from 55 studies across 35 countries to assess the occurrence, removal and ecological risks of antibiotics in municipal WWTPs and effluent-receiving water bodies. All major antibiotic classes - including β-lactams, quinolones, macrolides, sulfonamides, and tetracyclines - were consistently detected in influents, effluents, and receiving water bodies, often at concentrations ranging from tens to hundreds of thousands of nanograms per liter. Removal efficiencies exhibited substantial variability, with many WWTPs presenting low or even negative removal rates, underscoring limitations in the existing treatment technologies. Regional disparities were prominent, with Africa, Asia, and South America displaying the highest concentrations and widest variability, reflecting gaps in infrastructure, regulation, and antibiotic stewardship. Although Europe and North America generally exhibited lower contaminant levels, several facilities still reported incomplete removal, demonstrating that performance challenges persist globally. Ecological risk assessments revealed frequent exceedances of predicted no-effect concentrations (PNEC), with high-risk quotients (RQ) > 10 for ciprofloxacin, azithromycin, and sulfamethoxazole in effluents and receiving waters, signifying high-risk hotspots in Africa, Asia, and South America. These findings highlight the urgent need for coordinated action to enhance wastewater treatment performance, develop cost-effective advanced technologies, and strengthen regulatory frameworks.