: Good water management is literally vital for the arid and semi-arid regions of the planet. Yet good water management requires multidisciplinary expertise, since one must consider climatic, hydrological, economical and social aspects to make balanced decisions on water usage. We here present SegHidro, a grid portal designed to foster scientific, technical and operational collaboration, as to improve water resources management. The portal targets researchers and decision makers, enabling them to execute and couple their computational models in a workflow. The portal provides a framework which allows seamless integration of the models, meaning that each phase of the flow may be executed by a different expert and that the resulting data is shared among other portal users. Due to the nature of these applications and the need to execute many prospective scenarios, their execution requires high computing power. But we go beyond providing high performance computational grid capabilities. We ...