Invisible Infrastructure: A Systematic Review of Wastewater Disposal and Treatment in the Philippines (1982–2026)

Background: Wastewater disposal and treatment are critical but under-recognized components of public health and environmental protection infrastructure in the Philippines. Despite their importance, wastewater systems, treatment performance, and governance remain fragmented across decades of research and operational reporting. Methods: This study conducted a systematic review with narrative synthesis of wastewater disposal and treatment in the Philippines from January 1982 to 11 February 2026, following PRISMA 2020 guidelines. Major scientific databases and gray/institutional sources were searched using predefined eligibility criteria. Results: From 717 records identified, 582 were screened and 120 full texts assessed; 57 sources were included (39 empirical studies and 18 institutional or operational sources). National sector estimates indicate that only about 10% of wastewater is treated and approximately 5% of the population is connected to sewer networks, with most households relying on septic systems that frequently provide inadequate treatment. Empirical studies consistently link untreated wastewater to river degradation, groundwater contamination, heavy metal accumulation, eutrophication, and microbial pollution. Industrial and centralized treatment systems demonstrate high removal efficiency when properly implemented. Decentralized and nature-based systems, including constructed wetlands and hybrid biological technologies, show strong potential for scalable and cost-effective treatment, particularly in resource-constrained communities. Conclusion: Wastewater infrastructure in the Philippines remains uneven, with significant environmental and public health implications. Strengthening institutional coordination, investment, monitoring, and decentralized wastewater solutions is essential to improve wastewater sustainability and protect public health.