Vietnam declared its national roadmap towards Sustainable Development Goals number 6 by 2030. However, specific supporting programmes and financial means to proceed with the roadmap have not been passed on. Evidence on the financing for water, sanitation, and hygiene (WASH) being allocated or spent has not been well documented in Vietnam. This study aimed to obtain an overview and assessed the public funding across the WASH sector of Vietnam in 3 fiscal years 2016, 2017, and 2018. A cross-sectional study was conducted for information about the public financing for WASH at both national and sub-national levels. An activity-based costing approach was applied to determine WASH-related public expenditure. Fourteen focus group discussions with key stakeholders were used to identify the WASH activities and to access financial reports of these relevant institutions. TrackFin methodology was used to assemble the public financing for WASH in Vietnam.The public expenditure of WASH declined by about 30.7% over the 3 fiscal years, from US $2016 million in 2016 to US $1397 million in 2018. Meanwhile, this expenditure allocated to the poor or mountainous areas increased by 3 folds. The highest proportion of WASH public funding was invested in sanitation through large network systems (59.07% of the total public expenditure), whereas the lowest was in hygiene promotion and handwashing facilities. The domestic budget was still the main source of public financing for WASH services, with 2 largest shares coming from government revenues (47.24%) and repayable loans (20.49%).The main source of financing for WASH was from the government, yet its public expenditure has been decreased. A refined roadmap with specific steps for a sustainable WASH financing system in Vietnam, particularly to leverage government and private sector resources, is required to ensure no one is left behind.