The water heater powered by burning wood debris., it was a common contraption made in those days by buying a heavy base brass or copper large hundi and fix it inside the bathroom where the base of the vessel will be exposed from the outer wall of the bathroom through a chamber which will be laden with wood debris and daily in the morning the elderly would make an open spit fire and heat water in the vessel for bathing purpose as a result at single fill a family of 6 will be comfortably get heated water cost effectively, also the heat stays much longer and the water gets an unique smoky aroma.
The one is still operational and the fixed copper pot inside is 60 years old..it also doubles as an incinerator to burn dry kitchen debris and house hold throwaways there by fueling the water heater