AbstractWater security, as a Sustainable Development Goal, ensures that sustainable water supply is consistently available to every individual. A water supply systems (WSS) assessment matrix was designed as a tool for assessing WSS in low-income countries; with selected urban, peri-urban and rural Nigerian communities as case studies. Sustainability of the WSS was assessed through established criteria against five sustainability factors. Sanitary surveys were conducted to evaluate the risks associated with the WSS using sanitary inspection forms, through which the sanitary risk scores (SRS) were derived. For sustainability, the WSS were ranked as Very High, High, Medium and Low Sustainability, and for SRS as Very High, High, Intermediate and Low Risk. A Sustainability and Risk Assessment Matrix (SRAM) was designed using sustainability evaluation and risk assessment for the WSS. The WSS in the rural areas are more ‘Secure’ than those in urban and peri-urban towns, and boreholes are more ‘Secure’ than hand-dug wells, but none of the public water points are scored ‘Secure’. The paper concludes that SRAM provides a cost-effective method of classification and may serve as a pre-water quality and source sustainability assessment tool, especially in low-income countries, as part of the measures to achieve water security.