This review looks at how reusing water and desalination affect greenhouse gas emissions. They found that reverse osmosis technology causes less CO2 than thermal desalination. Seawater desalination has a larger carbon footprint (0.4–6.7 kg CO2eq/m3) than brackish water desalination (0.4–2.5 kg CO2eq/m3) and water reuse (0.1–2.4 kg CO2eq/m3), due to where they are, the tech used, and the stages considered. Different tools for estimating emissions can make it hard to compare accurately. If tools could separate emissions by type and consider resource recovery, they could be better.