Abstract
Water scarcity in arid and semi-arid regions relies on energy-intensive water treatment technologies, leading to increased greenhouse gas emissions. However, consistent cross-technology comparisons are limited. This study analyzed the carbon footprint of major water treatment systems and identified the key drivers of environmental performance. The authors reviewed 40 studies using a PRISMA-based approach and normalized the results to 1 m³ of treated water. The analysis includes seawater desalination, brackish water treatment, wastewater reuse, and conventional treatments. The carbon footprint varied from 0.07 to 24 kg CO₂-eq/m³. Thermal desalination exhibited the highest emissions (up to 24 kg CO₂-eq/m³). Reverse osmosis has lower values (approximately 1–4 kg CO₂-eq/m³). Wastewater reuse had the lowest impact, with emissions up to 79% lower than those of traditional thermal seawater desalination. Renewable energy reduces emissions by over 90%. Energy sources, salinity, plant scale, and chemical use drive these differences. These results highlight the need to integrate the water–energy–carbon nexus into water-supply planning. Wastewater reuse and renewable-powered desalination offer clear pathways for reducing environmental impacts in water-scarce regions. These findings directly support Sustainable Development Goal 6 (Clean Water and Sanitation) and Sustainable Development Goal 13 (Climate Action) by identifying low-carbon pathways for water supply in arid regions.