Safely managed wastewater is critical to water-related sustainable development. With a focus on the domestic wastewater component of SDG 6.3.1, this study reports that household activities worldwide generate 267.5 billion m3 yr− 1 of wastewater, of which 63% (168.8 billion m3 yr− 1) is collected in sewers and septic tanks, and 54.7% (146.3 billion m3 yr− 1) is treated. In comparison, 45.3% (121.2 billion m3) is released to the environment in untreated form, either uncollected (98.7 billion m3 yr− 1) or collected but untreated (22.5 billion m3 yr− 1). The monitoring of and progress on safely managed wastewater remain strongly uneven between the Global North and Global South and between geographic regions and income groups. While there is clear progress in the agricultural reuse of treated wastewater, untreated water reuse requires more attention. Considerable challenges remain because of terminology, informal irrigation, and the usefulness of reporting reuse volumes or areas for health-based targets.