Evaporation from oceans as well as other water bodies in the air and transpiration from land vegetation and animals into the air. Oxygen dihydride is another way of referring to water, but modern-day usage usually restricts the phrase "hydride" to ionic compounds (which water just isn't). Hydrology is the research https://kevalaniru.com/which-is-the-best-natural-mineral-water-brand-in-india-today/