The accurate determination of fluoride concentration in environmental and drinking water is critical for protecting public health and ensuring compliance with international water quality standards. In this study, a validated and efficient photometric method for fluoride quantification was developed using the Spectroquant Fluoride Test (Merck). The method is based on the reaction of fluoride ions with alizarin complex one and lanthanum (III) in a weakly acidic buffered medium to form a stable violet-colored complex, the absorbance of which is measured photometrically. The analytical procedure exhibits excellent sensitivity, selectivity, and precision across two quantifiable ranges: 0.10–2.00 mg/L and 1.0–20.0 mg/L F⁻, in accordance with EPA Method 340.3 and APHA Standard Method 4500-F E. Comprehensive validation was conducted to assess linearity, accuracy, and reproducibility, along with extensive interference studies covering common ions and organic substances. The findings confirmed negligible interferences under the optimized conditions, demonstrating the robustness of the method for diverse aqueous matrices. The reagents showed high chemical stability within the recommended storage conditions, maintaining consistent analytical performance over time. Owing to its simplicity, rapid execution, and low operational cost, this photometric approach represents a practical alternative to more complex techniques such as ion-selective electrodes and ion chromatography. The method’s applicability to groundwater, surface water, seawater, wastewater, and drinking water highlights its reliability as a universal tool for routine monitoring and regulatory compliance in fluoride analysis.