Service innovation and governance models for decentralised greywater systems in pro-poor urban settlements: evidence from Southlea Park, Zimbabwe

ABSTRACT This study develops the Greywater Service Innovation Ladder (GSIL), a governance-oriented framework for structuring the progression of decentralised greywater services in pro-poor settlements. Using Southlea Park, Harare, as a case study, the research demonstrates how measurable indices (Greywater Service Maturity Index (GSMI), Policy Readiness Score (PRS), Equity Safeguard Ratio (ESR) and Health Protection Targets (HPT)) translate policy aspirations into enforceable service thresholds. Baseline results revealed partial compliance, with affordability and health safeguards achieved, but weaknesses in policy, finance and monitoring limiting progression. Simulations showed that Gate 1 (household to community systems) could be attained through modest institutional reforms, while Gate 2 (community to utility grade) required systemic policy and financial restructuring. Comparative analysis confirmed alignment with global evidence that governance and equity, rather than technology, are decisive for scaling decentralised sanitation. The findings highlight GSIL's novelty as a decision-intelligence tool that embeds rollback mechanisms, ensuring accountability and preventing premature upgrading. Policy implications include embedding affordability caps, aligning thresholds with decentralisation frameworks and leveraging the GSIL as a benchmarking tool for investment and regulatory oversight. The study reframes sanitation ladders from descriptive models into computational decision frameworks, with practical relevance for Citywide Inclusive Sanitation (CWIS) and Sustainable Development Goal (SDG) 6.