What does desalination refer to?

Desalination is defined as the process of removing salt from saltwater, making it suitable for human consumption and irrigation. This process is essential in regions where freshwater is scarce, and salty water from oceans or seas is abundant. Methods commonly used in desalination include reverse osmosis and distillation, which effectively separate salts and other impurities from water, resulting in freshwater.

The other options do not accurately depict desalination. Adding salt to freshwater contradicts its purpose. Treating wastewater for agricultural use is an entirely different process involving recycling water, while purifying groundwater focuses specifically on improving the quality of water sourced from underground, not on removing salinity from saltwater sources.