Planners and decision-makers in the wastewater sector are often confronted with the problem of identifying adequate development strategies and most suitable finance schemes for decentralized wastewater infrastructure. This paper research has focused on providing an approach in support of such decision-making. It is based on basic principles that stand for an integrated perspective towards sustainable wastewater management. We operationalize these principles by means of a geographic information system (GIS)-based approach 'Assessment of Local Lowest-Cost Wastewater Solutions'--ALLOWS. The main product of ALLOWS is the identification of cost-effective local wastewater management solutions for any given demographic and physical context. By using universally available input data the tool allows decision-makers to compare different wastewater solutions for any given wastewater situation. This paper introduces the ALLOWS-GIS tool. Its application and functionality are illustrated by assessing different wastewater solutions for two neighboring communities in rural Jordan.