There is some salt in all water. Water on the land runs into lakes and rivers. The water from most lakes goes into rivers. These rivers run into the seas and oceans. They carry a little salt with them. Some of the ocean water moves into the air and clouds. But salt cannot move into the air. It stays in the ocean. So the water in the oceans has more salt than river water. Ocean water is about three and a half percent salt.

① Why Is the Sea Salty?                        

② How Much Salt Is in Water?

③ Why Does Water Go into Seas?          

④ Do All Seas Have the Same Salt?

⑤ How Does Water Move into the Air?