Earth formed by the accretion of countless small bodies ranging in size from pebbles to Nara-sized bodies. Some fraction of these planetesimals formed in the region where earth exists today (inner solar system) and likely had enough water to meet earths current inventory. Another probably smaller fraction of bodies from the outer solar system (like Ryugu and the other progenitors of CI chondrites) were also accreted and surely delivered some fraction to water. But to answer your question, earth was accreting water-bearing asteroids and planetesimals all throughout its accretionary history. It wasn’t a one-off event or even just a few random chance impacts.