Are those who work in seawater desalination plants that provide drinking water for Muslims rewarded for their work? Do they fall under the virtue of "providing water" if they seek the face of Allah? And is their work better than that of their colleagues in other fields, such as oil production?

Providing water is one of the best forms of charity. Sa'd ibn 'Ubadah, may Allah be pleased with him, asked the Messenger of Allah, peace and blessings be upon him, "Which charity is best?" He replied, "Water," so Sa'd dug a well for his mother. Working in water desalination plants is a communal obligation (fard kifayah) for which a Muslim is rewarded if they intend good by it, and taking wages for this work does not harm this reward.