Most of our water heaters are based on heating resistance coils. Not mention it takes minimum of 20-30 minutes to heat the water to 65 degrees. Why can't we use microwave or induction heaters,they will save at least 30-50% of energy and 50% of the time. Tanks can be constructed with stuff that is non conductor of heat there by retaining the heat for longer time. Warm water from solar concentrator can be fed instead of cold water,that needs to be further raised to 65 degrees.
There are instant heaters and regular heaters in the market. MW or induction heating will be very effective for instant heater types. Please let me know what you think.