The reaction of Al and H2O is a promising method for the renewable production of H-2 (an environmentally friendly fuel whose combustion produces only water), because it does not directly include fossil fuels conversion. This reaction was studied at extreme pH values as low as 1 and as high as 13.5 with HCl, H2SO4, and NaOH, and at low hydrothermal temperatures of 40-100 degrees C. Factors such as pH, temperature, and solution medium influenced H-2 production, which was considerably greater at higher temperatures and more extreme pH (acidic or alkaline). Alkaline conditions consistently favored more rapid H-2 production than acidic conditions. Under the most extreme conditions, the activation energy was similar to 60 kJ mol(-1) for both acidic and alkaline reactions. A model predicting H-2 production in acidic reactions was derived from the reaction mechanism and kinetics. The model yielded a good fit to on-site measurements at the Tamagawa and Zao hot springs in northeast Japan. This study would aid the development of industrial H-2 production systems using natural acidic hot springs or alkaline industrial wastewater. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.