<p>Arsenic contamination in drinking water remains a significant global health challenge, necessitating the development of low-cost and field-deployable sensing technologies. Most electrochemical sensors for arsenic rely on modified electrodes incorporating nanomaterials or complex fabrication processes, which limit their scalability and stability. Here, we demonstrate a highly sensitive and reproducible approach using a commercial, unmodified gold electrode coupled with Square Wave Voltammetry (SWV). Despite its simplicity, the system achieves remarkable sensitivity (33.06 µA⋅µM^− 1) and an exceptionally low limit of detection (LOD) of 0.045 µM ~ 3.37 ppb, which is significantly below the WHO limit (10&#xa0;µg⋅L^− 1), with excellent linearity (R² &gt; 0.99) across a broad concentration range. The robustness and accuracy of the linear calibration range (0.1 to 1.0 µM) were rigorously validated using chemometric methods (Unscrambler software), yielding a low root-mean-square calibration error (RMSEC) of 0.01, confirming the model’s excellent fit. Selectivity was rigorously evaluated against high concentrations of common interfering ions, and subsequent testing in real-world tap water samples confirmed the sensor’s practical utility. Critically, no significant interference was observed, unequivocally demonstrating high selectivity for arsenic. Compared to reported nanomaterial-modified systems, this unmodified approach provides a comparable combination of cost-effectiveness, reproducibility, and real-water reliability, marking advancement toward scalable on-site water quality monitoring and public health protection. </p> Graphical Abstract <p></p>