Heating water with a stove, microwave or kettle: what uses the least electricity?
If you want to heat water quickly and inexpensively, use the kettle. According to the Hausgeräte+ initiative, it clearly beats microwaves and pots with any amount of water. And kettles with built-in automatic shut-off protect against waste.
But the kettle is not always suitable. If you want to reheat soup instead of water, appliance experts recommend the microwave for small amounts up to about 500 milliliters.
From about a liter it will be cheaper in a jar. However, these quantities can no longer be microwaved without any problems anyway.