It depends on your answer - if you are talking about its creation, many scientists do believe that some meteorites which crashed into earth during the starting brought water along with them thus creating oceans. if you are speaking generally, then its all about rivers. melted ice from mountains form rivers which then flow into oceans
Ocean water comes from deep inside the earth.
Oceans don't come from anywhere. They were formed by gases, meteorites and other phenomenas that were present on Earth years ago. They are sourced by rainwater which is derived from them only.