Why is the Ocean Water Salty?
When the rain falls on the ground , salts from the soil and rocks dissolve in the water,
as it flows down through streams and rivers back to the ocean.
When this water evaporates from the ocean, the salt stays behind.
This cycle has been going on for more than a billion years. Resulting in the salty ocean water.

You can clearly guess that as this cycle continues the water in the oceans and seas will keep on getting more and more salty.