A kettle’s power consumption is proportional to the amount of water in it.
In the UK, the Energy Saving Trust conducted a survey of 86,000 homes. It found three-quarters of households overfill their kettle when boiling water. This wasted an additional £68 million pounds on electricity annually, and contributed to a larger environmental footprint (1).
According to Australian based Canstar blue, adjusting your habits is the most effective way of saving money and reducing power consumption (2).
This does not mean you need to drink less tea! Just fill your kettle with as much water as you need at that moment.