Auxiliary water-heater tank? ? ?
 

Recently I read somewhere that it's possible to add an auxiliary tank to
supply water heaters.

The purpose is, water comes from underground into a storage tank, where the
temperature of the water is raised by ordinary basement temperatures --
especially in furnace rooms.

This water then feeds water into the heating tank at a considerably higher
temperature, thereby saving energy costs.

This is common sense. Is this technology available now?