How salt water becomes fresh water

Evaporation is a natural distillation. It lifts water molecules and leaves dissolved salts behind — which is both why rain is fresh and why the sea is salty.

Why the sea is salty: Rivers deliver dissolved minerals continuously; evaporation removes only the water. Over hundreds of millions of years, salt concentrates.
Why rain is fresh: Evaporation is a phase change that only water molecules undergo. Dissolved ions are left behind.
Steady state: Ocean salinity is roughly stable because salts are removed by sediment burial and hydrothermal exchange at about the rate rivers supply them.

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Sea water evaporates, leaving salts behind in the ocean. Only water molecules enter the atmosphere, so cloud and rain are fresh. Rain falling on land dissolves minerals from rock, and rivers carry those minerals back to the sea, where evaporation removes the water but not the salt — so ocean salinity accumulates.