How is desalination commonly carried out?

Desalination is the process of removing salt and other impurities from seawater or brackish water to obtain fresh water suitable for human consumption and irrigation. The method of reverse osmosis is widely used in modern desalination processes, where water is forced through a semipermeable membrane that allows water molecules to pass while blocking the majority of salt ions and other contaminants. This method is efficient and energy-effective compared to some other methods.

Distillation is another common technique in which seawater is boiled to produce steam, which is then condensed back into a liquid, leaving behind salt and impurities. This process relies on the fact that salts and minerals have higher boiling points than water, thus separating them when the water evaporates.

The option indicating direct evaporation would not be as efficient because it would not ensure complete removal of all salts and could be significantly slower depending on environmental conditions. Boiling and freezing is not a practical mass-scale method for desalination, as it may not effectively yield pure water and involves additional complexities in handling phase changes. Chemical precipitation typically involves the addition of chemicals to cause dissolved substances to form solid particles, which is not a standard method for removing salts from water in desalination processes.

Therefore, the combination of reverse osmosis and