There is increasing awareness of household self-supply and the role it can play in securing water for domestic needs in low- and middle-income countries (LMICs), but its scale across the Asia-Pacific has not previously been quantified. This study analysed 77 datasets from 26 countries to estimate the prevalence of self-supplied drinking water, and its associated trends in LMICs in South Asia, Southeast Asia and the Pacific. When factoring in temporal trends, results suggest that >760 million people—or 31% of the population—relied on self-supply for their drinking water in these regions in 2018, with the number of users increasing by >9 million each year. Reliance on self-supply for drinking water is greater in rural areas than in urban areas (37% of rural population vs 20% of urban population), though results vary considerably between countries. Groundwater sources constitute the most common form of self-supply in South Asia and Southeast Asia, while rainwater collection is dominant in the Pacific. The results confirm the significance of self-supply in the Asia-Pacific and suggest that households are a major but often overlooked source of financing within the water sector. The findings raise important questions about how policy and practice should respond to this widespread phenomenon.