In this study, the possibility of ²²²Rn removal through the deferrization/demanganization applied for water treatment was considered, assuming a sorption process. This study demonstrates the possible removal of dissolved radon from groundwater using manganese oxide sand (MnO₂) employed in conventional water treatment systems. Four groundwater samples with varying chemical compositions were treated, and the simultaneous removal of ²²²Rn, Mn²⁺, Fe²⁺, NH₄⁺, and NO₃⁻ was evaluated. Radon activity was quantified using a Lucas scintillation cell coupled with a Pylon AB-5 system, while inorganic ions were analyzed by ion chromatography. Structural characterization of MnO₂ sand by XRD, SEM–EDS, and FTIR confirmed a heterogeneous oxide surface favorable for adsorption. The treatment achieved average removal efficiencies of 95% for ²²²Rn, 79% for Mn²⁺, 87% for Fe²⁺, 85% for NH₄⁺, and 73% for NO₃⁻. Equilibrium adsorption capacities increased with initial contaminant concentrations, indicating a multi-species uptake. Importantly, radon removal was largely independent of coexisting ions. These results reveal the benefit of MnO₂-based water treatment, offering an effective solution for simultaneous radon and inorganic contaminant mitigation.