The water evaporates gradually, if enough temperature is maintained.
Evaporation happens when a liquid substance becomes a gas. When water is heated, it evaporates. The molecules move and vibrate so quickly that they escape into the atmosphere as molecules of water vapour.
The change is more palpable if it occurs in just a small amount of water- such as a spill of a drink in the floor rain a piddle ets- but with cases such as lakes, oceans and the like, the change is most likely unnoticrable.