I don't do this, but I'm impatient so I start with scalding hot tap water. Not sure if there is any energy saving (or waste) there, since it takes at least 30 sec for hot tap water to reach max temp.
If you have lead in your pipes, the hot water will have more lead dissolved in it and boiling isn't going to remove it. You can use try filling your pot one rapid boil tea kettle at a time, or try an induction hob.
The potential for energy saving is if your hot water service is significantly more energy efficient than your stove top. The most extreme would be if you had a heat pump hot water service and a gas flame stove top.
Also important for efficiency and speed is to use the least amount of water possible.
