Bali is confronting severe water stress exacerbated by tourism expansion, climate change, and population growth, with around 60% of the island facing seasonal water scarcity. Traditional management methods fail to reconcile tourism revenue with freshwater conservation. This study proposes an integrated computational framework combining Grey Relational Analysis (GRA) and Multi-Objective Decision-Making (MODM) to optimize water governance. The GRA module quantifies critical correlations between water use and tourism indicators under data-scarce conditions, identifying tourist volume as the primary driver. The MODM model then pursues dual objectives—maximizing tourism income while minimizing freshwater consumption—through optimized visitor numbers, progressive water taxes, and strategic promotion of low-water-intensity activities. The solution achieves a 23.7% reduction in water use while maintaining robust economic returns. Supported by IoT and remote sensing, this approach provides a dynamic, scalable strategy for sustainable water management in tourism-intensive regions.