This study examines the impact of ferric iron contamination in mixing water on the bending and shears strength of reinforced concrete beams, addressing a critical yet explored durability concern in modern concrete construction. Although ferric iron is a common contaminant in tropical groundwater, its structural implications remain insufficiently quantified compared to chloride or sulfate ions. The research aims to bridge this gap by experimentally assessing how ferric iron-laden water alters the flexural and shear behavior of reinforced concrete beams. Three beams were cast using a 1:2:4 mix ratio and a constant water–cement ratio of 0.6, two with ferric-iron-contaminated water (5.3–12.3 mg/L Fe³⁺) and one with potable control water, were tested under four-point loading after 28 days of curing. Parameters measured included yield load, deflection, failure load, bending capacity, and failure mode. Results revealed that ferric-iron-contaminated beams exhibited increased deflection, reduced stiffness, and wider cracks relative to the control, indicating stiffness degradation, early corrosion, and loss of bond integrity at the steel–concrete interface. Although one ferric beam attained a slightly higher ultimate load, its larger deformation signified reduced elastic modulus and premature ductility loss. These findings establish that ferric iron contamination significantly compromises both bending and shear performance by altering hydration chemistry and promoting corrosion expansion within the concrete matrix. The implications are far-reaching for construction practices in groundwater-dependent regions, emphasizing the urgent need for water-quality assessment and regulation in concrete production. This study contributes empirical evidence for refining mixing-water standards and calls for sustainable engineering policies to mitigate corrosion-induced failures in reinforced concrete structures.