The development of technologies that would lead toward the adoption of a hydrogen economy requires readily available, safe, and environmentally friendly access to hydrogen. This can be achieved using the aluminum−water reaction; however, the protective nature and stability of aluminum oxide is a clear detriment to its application. Here, we demonstrate the spontaneous generation of hydrogen gas from ordinary room-temperature tap water when combined with aluminum−oleic acid core−shell nanoparticles obtained via sonochemistry. The reaction is found to be near-complete (>95% yield hydrogen) with a tunable rate from 6.4 × 10−4 to 0.01 g of H2/s/g of Al and to yield an environmentally benign byproduct. The potential of these nanoparticles as a source of hydrogen gas for power generation is demonstrated using a simple fuel cell with an applied load.