Water consumption is a critical factor in evaluating the sustainability of hydrogen systems. While much attention focuses on carbon emissions, the total lifecycle water use—spanning production, storage, and transport—reveals additional challenges and opportunities for conservation. Different production methods, such as steam methane reforming (SMR) and electrolysis, exhibit varying water footprints, and storage or transport pathways introduce further demand. Identifying hotspots in these systems enables targeted efficiency improvements without compromising scalability.
Steam methane reforming, the dominant industrial method for hydrogen production, requires significant water inputs primarily for two purposes: process steam generation and cooling. The reaction itself consumes water stoichiometrically, with approximately 2.5 to 5 liters of water per kilogram of hydrogen produced. However, when accounting for auxiliary processes such as natural gas extraction, purification, and plant cooling, the total water footprint can escalate to 10–20 liters per kilogram. SMR facilities often rely on once-through or recirculating cooling systems, with the latter reducing withdrawal but increasing consumption due to evaporative losses. In regions with water scarcity, this poses a sustainability challenge, particularly if freshwater sources are prioritized over treated wastewater or saline alternatives.
Electrolysis, particularly when powered by renewable electricity, presents a different water profile. The theoretical minimum for alkaline or PEM electrolysis is around 9 liters of water per kilogram of hydrogen, as dictated by the stoichiometry of water splitting. In practice, purification, cooling, and balance-of-plant needs raise this to 15–25 liters per kilogram. High-purity water is essential to avoid electrode degradation, adding energy and cost for pretreatment. However, electrolysis offers flexibility in sourcing, including the potential for seawater use with advanced desalination, albeit at higher energy penalties. Unlike SMR, electrolysis avoids water-intensive feedstock extraction, shifting the burden to the energy supply chain. For instance, renewable-powered electrolysis inherits the water footprint of photovoltaic or wind infrastructure, which is generally minimal but non-negligible in concentrated solar power with wet cooling.
Storage and transport introduce secondary water demands often overlooked in standalone production analyses. Compressed gas systems require energy for compression, often sourced from electricity with its associated water footprint in generation. Liquid hydrogen storage, while efficient in energy density, consumes additional water for cryogenic cooling—up to 30–50 liters per kilogram when accounting for power plant cooling loops. Chemical carriers like ammonia or liquid organic hydrogen carriers (LOHCs) reduce transport losses but add water in their synthesis and dehydrogenation steps. Ammonia production via the Haber-Bosch process, for example, uses 0.5–1.5 liters of water per kilogram of ammonia, which then carries roughly 0.18 kg of hydrogen.
Transport infrastructure further compounds water use. Pipeline networks, while efficient for bulk delivery, require periodic maintenance and leak detection, often involving water-intensive cleaning or pressure testing. Truck and rail transport of compressed or liquid hydrogen rely on diesel or electric propulsion, indirectly linking to the water footprint of fuel extraction or power generation. Maritime shipping of ammonia or LOHCs may have lower operational water costs but must account for port facilities and carrier synthesis.
Hotspots for conservation emerge clearly across these systems. In SMR, shifting to dry cooling or wastewater reuse in steam generation can reduce freshwater withdrawal by 50% or more. Electrolysis plants can integrate direct air capture or seawater desalination to avoid competing with municipal or agricultural needs, though energy efficiency must be monitored. Storage innovations such as advanced metal hydrides or adsorption materials may reduce reliance on energy-intensive compression or liquefaction. For transport, optimizing routes and modes—such as prioritizing pipelines over trucks in high-demand corridors—can lower both energy and water overhead.
A comparative summary of water use highlights key trade-offs:
- SMR: 10–20 L/kg H2 (primarily from steam and cooling)
- Electrolysis: 15–25 L/kg H2 (from purification and auxiliary systems)
- Liquid H2 storage: +30–50 L/kg H2 (from cryogenic cooling energy)
- Ammonia carrier: +0.5–1.5 L/kg NH3 (from synthesis)
The choice between these methods hinges on regional water availability as much as energy costs or emissions. Arid regions may favor electrolysis with dry cooling or non-freshwater sources, while water-rich areas could prioritize SMR with closed-loop cooling. Hybrid systems, such as solar-thermal assisted electrolysis, may further decouple water demand from production rates by time-shifting energy inputs.
Ultimately, lifecycle water use in hydrogen systems is not a fixed metric but a variable shaped by technology choices and operational practices. Conservation strategies must extend beyond production to encompass storage and transport, ensuring that the hydrogen economy advances without exacerbating water stress. Innovations in material science, renewable integration, and circular water use will be pivotal in achieving this balance.