The lithium hydride-water reaction was studied using a novel flow calorimeter to determine the mechanism and thermodynamics of lithium compound-water interactions at elevated temperatures. A concomitant consideration of heat and hydrogen evolution data led to a simple physical reaction model for temperatures of 505 and 588 K. Initially, water interacts directly with lithium hydride to form lithium oxide and hydrogen. However, the lithium oxide surface layer which forms via this reaction subsequently reacts with additional water to form lithium hydroxide. The net effect of this mechanism is that both heat and hydrogen evolution decline per amount of water injected in a batch-type reaction system.