Onsite wastewater treatment systems (OWTS) are a widely used and cost-effective method for managing household wastewater in the United States, especially in rural and coastal areas. In Gulf-adjacent states, an estimated 20–40% of residents depend on OWTS, with the highest reliance observed in coastal regions. While many systems operate reliably for decades, failure rates may reach up to 40%, suggesting OWTS could contribute more significantly to water pollution than previously recognized. This risk is further amplified by climate-related stressors such as extreme weather events and sea-level rise. Historically, the lack of comprehensive OWTS location data in the Gulf Region has hindered efforts to evaluate their environmental impact. This presentation highlights ongoing initiatives aimed at improving our understanding of OWTS-related nutrient loading in Gulf waterways, including: (1) building a national inventory of publicly available OWTS data and acquiring proprietary datasets, (2) applying machine learning to estimate OWTS densities, (3) modeling pollution potential to identify high-risk areas, and (4) optimizing spatial planning for future infrastructure development. With improved data and modeling, decision-makers are better equipped to craft targeted regulations and resource allocations that address OWTS-related nutrient loading.