What is the most energy efficient way to keep a cup of water warm?

Question

I need to keep some warm water available all day.

It seems like a waste to run the cold water till it turns warm from the faucet each time I need it.

The other option would be to keep a tea kettle on the gas stove turned low.

Another option is one of those table top mug warmers.

I'm just wondering what the best and most energy efficient way to keep water warm is.

Answer 1

Buy a Stanely thermos.  Fill it with hot water in the morning and it will keep you water warm all day.

Answer 2

i dont know,,, maybe you could set it in the sun?

Answer 3

This might do the trick:

http://www.quickcup.co.uk/