1. A WATER HEATER FOR HEATING WATER AS IT FLOWS THROUGH THE HEATER, COMPRISING A CONTAINER, A SALT DISPOSED IN SAID CONTAINER AND CAPABLE OF STORING HEAT WHEN PASSING FROM THE SOLID TO THE MOLTEN STATE AND CAPABLE OF RELEASING HEAT OF CRYSTALLIZATION WHEN PASSING FROM THE MOLTEN TO THE SOLID STATE, MEANS TO HEAT SAID SALT TO A TEMPERATURE ABOVE THE MELTING POINT THEREOF, A WATER CONDUIT EXTENDING INSIDE THE CONTAINER AND SURROUNDED BY SAID SALT FOR CARRYING WATER THROUGH THE CONTAINER TO SUPPLY HEAT TO THE FLOWING WATER FROM THE SALT, AND MEANS TO AUTOMATICALLY SHUT OFF SAID HEATING MEANS WHEN SAID SALT IS SLIGHTLY ABOVE ITS CRYSTALLIZATION TEMPERATURE AND TO AUTOMATICALLY TURN ON SAID HEATING MEANS WHEN SAID SALT IS SLIGHTLY BELOW ITS CRYSTALLIZATION TEMPERATURE, SAID SALT MAINTAINING A SUBSTANTIALLY CONSTANT TEMPERATURE FOR HEAT TRANSFER DURING CRYSTALLIZATION FROM THE MOLTEN STATE AND WITH THE HEATING MEANS SHUT OFF.