I personally think the water came from various sources. Plus there’s the fact that 67P/Churyumov–Gerasimenko is a very short term comet and probably doesn’t represent all comets well.
The water came from a rain delay during a Cubs game in Chicago...thought it would never stop...
Carbonatous chondrite meteors where made our of the same “dust” that the earth was. In fact, these meteors can be up to 22% water. So the ones that still occasionally strike us, along with a chondrites, tell us about the composition of earth and we have had water since very soon after our formation. Now, if the “Big Thwack” theory of the moon is correct, and the moon samples support that theory of our collision with “Thera” creating the moon, the collision would have blown any surface volatiles off into space. The great bombardment periods along with volcanic activity would have replaced and added to the atmosphere and oceans.
Anyhow, that’s the theory many geologists have. :-)