The water footprint of hydrogen production

Hydrogen (H₂) is the most promising energy carrier for reducing the carbon emissions of the energy sector, but the impact of its production on water resources remains unclear. Here, we quantify the water footprint (WF) of different H₂ production pathways accounting for the WF of the primary energy used in the production process, as well as feedstock and infrastructure water requirements. Results suggest that green H₂ obtained from water electrolysis powered by renewable energy has the lowest WF (65 ± 2 m³/TJ for wind and 204 ± 79 m³/TJ for solar) mostly due to the low WF of renewable energy. The WF of blue H₂ derived from fossil fuels is significantly higher (369 ± 30 m³/TJ for natural gas and 564 ± 82 m³/TJ for coal) due to high WF of fossil fuels as well as the water required for carbon capture and storage (CCS). H₂ produced from nuclear energy and biomass have extremely high WF (741 ± 277 m³/TJ for nuclear and > 50,000 m³/TJ for biomass). Considering global and country-based energy scenarios, where the main H₂ colors (green and blue) individually account for 15 % of energy consumption, we find that the use of green H₂ could reduce the water demand of the energy sector while blue H₂ would generally increase it, except in countries already characterized by high water consumption due to reliance on water-intensive energy sources. At the global level, we find that for every 5 % of H₂ energy adoption, the energy sector could have water savings between 1 and 4 % for green H₂ and increase water consumption between 1 and 5 % for blue H₂. These results highlight the potential and criticalities of H₂ within the water-energy nexus.