The fundamental question is whether water is a fundamental human right, or a commodity; a privileged service that you can only access if you can afford it.
Article 25 of the United Nations Declaration of Human Rights—the premier human rights doctrine that practically all nations have signed up to—notes the following:
“Everyone has the right to a standard of living adequate for the health and well-being of himself and of his family, including food, clothing, housing and medical care and necessary social services, and the right to security in the event of … circumstances beyond his control.”
— Universal Declaration of Human Rights, United Nations, December 10, 1948
While water is not mentioned explicitly, the right to food includes water as well, because water is essential for humans to live, and is therefore in line with the principles of the declaration.