This study investigates the future cost and performance of three water electrolysis technologies—alkaline (AEC), proton exchange membrane (PEMEC), and solid oxide electrolysis cell (SOEC)—through expert elicitation. Experts estimate that increased R&D funding could reduce capital costs by 0–24%, while production scale-up alone could reduce costs by 17–30%. System lifetimes may converge at 60,000–90,000 hours, with negligible efficiency improvements. Experts highlight the need for improved production methods, automation, and higher quality components. Research into SOECs with lower electrode polarization resistance or zero-gap AECs could challenge PEMEC dominance. The study shows that expert elicitation can guide investment, policy, and research to support low-carbon energy systems. AEC is currently the dominant technology, but PEMEC is expected to become more prevalent by 2030 due to its flexibility and efficiency in intermittent operation. SOEC is less developed but has potential for higher efficiency and lower costs with material innovations. Production scale-up is more impactful on cost reduction than R&D funding alone. Experts estimate AEC costs at 750–1000 €/kW_el by 2030, PEMEC at 850–1650 €/kW_el, and SOEC at 1050–4250 €/kW_el. Lifetime estimates range from 40,000 to 110,000 hours for AEC, 40,000–85,000 hours for PEMEC, and 50,000–100,000 hours for SOEC. Efficiency improvements are expected, with zero-gap AEC and PEMEC systems potentially outperforming traditional systems. The study emphasizes the importance of production methods, product standardization, and operational experience in reducing costs and improving performance. Expert elicitation provides valuable insights for future investment and policy decisions in low-carbon energy systems.This study investigates the future cost and performance of three water electrolysis technologies—alkaline (AEC), proton exchange membrane (PEMEC), and solid oxide electrolysis cell (SOEC)—through expert elicitation. Experts estimate that increased R&D funding could reduce capital costs by 0–24%, while production scale-up alone could reduce costs by 17–30%. System lifetimes may converge at 60,000–90,000 hours, with negligible efficiency improvements. Experts highlight the need for improved production methods, automation, and higher quality components. Research into SOECs with lower electrode polarization resistance or zero-gap AECs could challenge PEMEC dominance. The study shows that expert elicitation can guide investment, policy, and research to support low-carbon energy systems. AEC is currently the dominant technology, but PEMEC is expected to become more prevalent by 2030 due to its flexibility and efficiency in intermittent operation. SOEC is less developed but has potential for higher efficiency and lower costs with material innovations. Production scale-up is more impactful on cost reduction than R&D funding alone. Experts estimate AEC costs at 750–1000 €/kW_el by 2030, PEMEC at 850–1650 €/kW_el, and SOEC at 1050–4250 €/kW_el. Lifetime estimates range from 40,000 to 110,000 hours for AEC, 40,000–85,000 hours for PEMEC, and 50,000–100,000 hours for SOEC. Efficiency improvements are expected, with zero-gap AEC and PEMEC systems potentially outperforming traditional systems. The study emphasizes the importance of production methods, product standardization, and operational experience in reducing costs and improving performance. Expert elicitation provides valuable insights for future investment and policy decisions in low-carbon energy systems.