If you're reboiling water aren't you already doing it wrong.

Ideally you should only be boiling the water you need.

I don't have reverse-osmoze filters, so I get pretty much residue (lime) which I rather leave in the kettle.

Moreover I sometimes want to add extra hot water to my 0,5L cup of tea. When boiling water, I already add the extra water I'll need so I get it just-in-time (except it has already lost much heat thus why I'll try to get insulated kettle). My wife may or may not want to drink tea, but I get ready water anyways (yeah, this could be organized better)

I just have a thermos flask next to the kettle. The excess ALWAYS gets put to good use: extra cups of tea (without reboiling), cooking, dishes in the sink, or even the kids' bath.

Throw a kitchen towel over the kettle after you pour off your first drink.