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This study addresses the need for simple and cost-effective predictive models for the design and operation of constructed wetlands in domestic wastewater treatment. The objective was to formulate and validate mathematical models describing the dynamics of Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD), and Dissolved Oxygen (DO) in a horizontal subsurface flow wetland planted with Typha Domingensis. The models were derived from mass balance equations and first-order degradation kinetics, and validated experimentally under different hydraulic retention times (HRT) ranging from 3 to 15 days. The results showed removal efficiencies above 90% for COD and BOD when HRT≥5 days, while DO exhibited higher variability, influenced by both biological and physical processes. The best predictive performance was obtained for DO (R2 up to 0.835), whereas COD and BOD fits were moderate. A stability condition was identified, expressed as Q>VkDO, which ensures sustainable aerobic operation of the wetland. The findings demonstrate that first-order models, despite their simplicity, provide a practical and low-cost tool for the design and optimization of constructed wetlands in low-resource contexts, with potential for integration into decentralized sanitation strategies. Future improvements could be achieved by incorporating additional variables such as temperature, pH, and microbial activity.