Question: how many kwh does it take to boil 1 litre of water?
Answer: Again, heating of 1 litre of water from 20oC 100oC need 330kJ (0.091kWh) of heat. All these method provide the this amount of heat to water. If you look the kettle which will have about 90% effciency, require 0.183kWh of electricty.