The first two or three years after we moved into this house in 1957, the hot water came from the oil-fired boiler, the same as the baseboard heat. The equipment was original to the homes construction in 1952. My parents were not satisfied with this arrangement, so had an 80 gallon Rheem electric water heater installed in 1960 or 61. This proved to be much better.
Separate electric meters for water heaters were not used in my immediate area, nor anywhere in CG&E (now Duke Energy) territory to the best of my knowledge. However, DP&L (Dayton, OH) did use them. Some family friends that lived several miles away were in the DP&L area, and their house had this meter arrangement. It consisted of three meter sockets. One held a meter for the regular house load, another for the WH time switch, and the other a meter for the WH. This of course required a separate disconnect and circuit breakers for the water heater. There was a good illustrated explanation of this type of system in the older editions of the Wiring Simplified book by H.P. Richter. I don't know if the newer editions have this or not