Arsenic contamination in drinking water poses a critical environmental and public health threat, particularly in rural areas such as Huanuara, Peru, where concentrations exceed the 10 µg·L⁻¹ limit established by the World Health Organization (WHO). This study explores the potential use of iron-rich metalworking residues as an alternative adsorbent. Characterization using Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM–EDS), X-ray Diffraction (XRD), and Brunauer–Emmett–Teller (BET) analysis revealed a specific surface area of 0.7469 m²·g⁻¹, with magnetite (Fe₃O₄) and metallic iron (Fe⁰) as the predominant phases. Arsenic concentrations were quantified by Inductively Coupled Plasma Mass Spectrometry (ICP–MS). A batch reactor system treated 16 L per cycle under conditions of 293–298 K and 95.46 kPa. Adsorption parameters were optimized using a Central Composite Rotatable Design (CCRD), with adsorbent mass (31.72–88.28 g) and contact time (4.17–9.83 h) as variables. Under optimal conditions (80 g, 9 h), 99.07% arsenic removal was achieved, reducing concentrations from 530.03 µg·L⁻¹ to ≤4.91 µg·L⁻¹. The quadratic regression model (R² = 0.90, p = 0.0006) was validated by ANOVA (p < 0.05; F = 22.02). These results demonstrate that metalworking residues offer a scalable and sustainable solution for arsenic remediation, supporting circular economy principles and decentralized water treatment.