We examine vertical and horizontal water governance interactions for their effect on water sustainability. This focus is important due to the role of resource governance in achieving sustainable outcomes. Climate change and variability heighten the urgency for better understanding the various facets of governance interactions. Data obtained through semi-structured interviews, document reviews, direct observation, and review of archival records were triangulated to ensure a robust analysis. Textual data were analyzed using initial and focused coding methods. Results show that the avenues for interaction across state, regional, and local levels all relate to the state's Groundwater Management Act (GMA), either in how the Act is interpreted or from its specific mandates. Horizontal governance interactions were either cooperative, based on shared interests on supply augmentation for growth, or contentious due to shared groundwater basin. We found that the (in)ability to achieve sustainable water governance at the local and regional levels was as much a result of vertical governance as horizontal governance. Specifically, interactions across levels are mostly statutory and not cooperative in achieving robust water sustainability, while success through horizontal governance is hindered by dissatisfaction over groundwater management, growth visions, and exempt wells.