Water does go back to the earth but not as clean as it started. Most water has been contaminated with herbicide/ pesticides run off, industrial waste and/ or pharmaceutical drugs. Not to mention micro plastics, heavy metals, detergents, etc.
Fresh and clean drinking water is a limited resource, in many places there is simply too much pollution. So while it can be “reused” it would require a lot of remediation to create the same quality water it originally was.
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