Unlocking global rainwater harvesting potential for safe drinking water access

Sustainable Development Goal (SDG) 6.1 aims for universal access to safely managed drinking water (SMDW) by 2030, yet progress remains off-track with 2.2 billion people lacking these services. Our comprehensive global analysis revealed a striking paradox: 88.5% of those without SMDW resided in regions with abundant rainfall, while only 1.26% used rainwater for potable use. Accordingly, a parametric framework integrating environmental and socioeconomic indicators was developed to quantify rainwater harvesting (RWH)'s potential for advancing SDG 6.1. This framework enabled a stepwise, actionable roadmap centered on two synergistic pathways: extending maximum seasonal storage potential and improving transition ratios, with simulations demonstrating that progressive optimization of RWH could increase SMDW coverage by 5.6-26%, benefiting 0.45-2.08 billion people. Socio-ecological analyses further showed that RWH supported multiple SDGs, including food security, health, gender equality, and climate action. These findings establish a systematic global assessment for unlocking vast untapped rainwater potential, providing important pathways that could fundamentally accelerate the achievement of universal SMDW access.