Greetings from Japan. The Japanese have perfected bathing technology. Filling and reheating the bath (called, oidaki) are accomplished via digital control panels. The bath water is circulated to an outdoor gas boiler through separate supply and return pipes leading. A charming lady lets you know when your bath is almost ready and a little tune plays to tell you when to get in!
FYI: the bath water is changed every few days and the whole family shares this water. There is always a shower adjacent to bath, so everyone must make themselves very clean before getting in. When not in use, the batch has an insulating lid to keep the water as warm as possible.
In the winter most Japanese take a bath every day (particularly when they get home from work).