Why is the water in the sea salty?

About film

A fisherman caught a single fish. As he walked home through the forest, he met a Leshy, who was in trouble. The fisherman helped him, shared his fish, and in return, for his kindness was rewarded from Leshy with a little mill. The mill can both grind salt and provide any food, so long as one knows the proper way to request it. The fisherman started to live well. But the happiness of others wakes envy. A merchant stole the little mill to grind salt. However, his extreme greed was punished – he drowned along with his ship. And the little mill continues to work at the bottom of the sea - that’s why the water in the sea is salty.