The availability of freshwater and low-cost electricity are two limiting factors for sustainable living in Hawai'i and worldwide. This fact raises the question: Can technology be developed to locate freshwater and geothermal resources simultaneously? We present a multimodal machine learning (MML) workflow to assimilate and simultaneously predict the 3d distribution of numeric and categorical features (field observations) along a groundwater-geothermal continuum. Success of the MML workflow relies on a transductive learning algorithm that projects field modalities onto a single embedding space (hypersurface). Multimodalities can include any combination of measured (point field) and derived (multiphysics-based numerical model inversions, data-driven machine learning, and multiphysics-informed machine learning) features. The proposed MML workflow is applied to assimilate randomly shuffled subsets of Hawai'i Play Fairway modalities and predict subsurface geophysical, geologic, and hydrogeologic features at the Islands of Lāna'i and Hawai'i. Despite challenging field data characteristics (disparate, scale dependent, spatially limited, sparse, and uncertain), the MML workflow yields a single 3d transdisciplinary model that generalizes well to independent data presented to the trained model. The predicted features are used to identify hidden groundwater and geothermal resources at Lāna'i, and geothermal resources at Hawai'i. Other interpreted subsurface features at Lāna'i include basalt, batholith, dike swarm, pluton, sill, mantle, Moho, and 3d geothermal stratigraphic units; whereas interpreted subsurface features at Hawai'i include 3d velocity layering, 3d earthquake-fault associations, 3d fault systems; basalt, oceanic crust, magmatic underplating, lithospheric flexure, mantle, and Moho. This study provides new capabilities for characterizing continuous subsurface groundwater and geothermal features for sustainable living in the Hawai'ian Islands and other geothermal sites worldwide. Keywords: Multimodal machine learning, 3d geothermal stratigraphic units, 3d hidden groundwater resources, 3d hidden geothermal resources 3d velocity layering, 3d earthquake-fault associations, 3d fault systems; basalt, batholith, dike swarm, oceanic crust, pluton, sill, magmatic underplating, lithospheric flexure, mantle, Moho, Island of Lāna'i, Island of Hawai'i