The paper presents an application of the new version of the 'Decision Support for Irrigated agriculture' DSIrr designed to integrate water and agricultural policy analysis and to support participatory decision process. The tool is a scenario manager for bio-economic farm models considering climatic, agronomic, hydraulic, socio-economic and environmental aspects. The paper offers some insight on the decomposition approach adopted to integrate economic analysis at different scales by illustrating a case study conducted in Italy to support an ex ante evaluation of a water management system reorganisation. Reduce water consumption is a strategic objective which pricing policy cannot address given technical constraints. The replacement of the existing low-efficiency irrigation system could be the solution, but the recover of cost creates an affordability problem. Results suggest that a dual network, integrating agricultural and rural urban sectors, represents a real challenge for the Irrigation Board since this option meets the environmental goal and pass the economic sustainability test.