Cheapest way to heat small amount of water

JennyW_2

In the mornings I only need a small amount of hot water (about half a pint). Now is it cheaper to just boil this amount in the kettle or run the tap until the boiling water comes out? (Have a Combi boiler).

I sort of think the kettle would be cheaper than running the boiler long enough to get this amount of hot water?

x_raphael_xx

Boiling a kettle with just the water needed would be cheaper than running the boiler.
I never switch my boiler on, I have an electric shower & fill up a kettle for hot water to do the dishes.