Evaluating the role of national income in sanitation, water, waste, and health access across multiple countries

Flowchart linking GNI to water supply and sanitation, waste generation, and 2019 mortality rate; results show GNI relates closely to these indicators in lower-income countries but weakly in higher-income ones, and mortality falls as GNI rises. Equitable access to water, sanitation, and hygiene (WASH) and effective waste management are crucial for meeting Sustainable Development Goals (SDG)s 6 and 12.5, yet few studies explicitly isolate the role of national income across development contexts. This study fills that gap by analysing how gross national income (GNI) relates to WASH access, household waste generation, and WASH-attributable mortality across 12 countries representing four World Bank income groups (2013–2022). Country-level linear regressions used GNI as the predictor for drinking water and sanitation coverage, household waste (tonnes), and deaths per 100,000 from unsafe WASH, and results reveal a clear income gradient. In low-income contexts, GNI strongly predicts gains in WASH access (R2 up to 0.991 for sanitation and 0.980 for drinking water) and higher mortality burdens (up to 99.2 deaths/100,000), while high-income contexts show saturation (sanitation R2 as low as 0.032) and minimal mortality (<4/100,000). Household waste rises with income in lower-income settings (R2 up to 0.654) but stabilizes or falls at higher incomes (R2 ≈ 0.644). Implications: economic growth bolsters fiscal capacity for WASH expansion, but diminishing returns at higher incomes mean policy, governance, and equity interventions are essential to secure sustainable, equitable outcomes.