Water circularity in Power-to-X: strategies for integrating water reuse into emerging energy systems

Power-to-X (PtX) processes are gaining attention as pathways to store renewable electricity in the form of hydrogen, synthetic fuels, and chemicals. While PtX technologies support decarbonisation and energy system flexibility, sustainable water management is increasingly recognised as a key constraint for large-scale deployment. This review synthesises recent literature on water demand and quality requirements across PtX pathways and identifies opportunities for circular water strategies, including integration with wastewater treatment, advanced water recovery, and internal reuse. Water availability, feedwater quality, purification requirements, energy penalties, and governance frameworks are identified as critical factors shaping water circularity in PtX systems. Although conventional water purification typically contributes less than 1% to the levelized cost of hydrogen (LCOH), water availability and sourcing constraints can emerge as system-level limiting factors, particularly in water-stressed regions. Key research gaps include electrolysis performance under circulating and reclaimed water operation, and system-level modelling that accounts for water scarcity and intermittent operation