This may sound like a silly question, but I've always wondered:

If I boil some water and use some of it and leave the remainder in the kettle, and then a few days later boil that same water again, will it taste the same as if I'd emptied the old water and boiled fresh new water?

I've got a habit of emptying the kettle water and starting with fresh water to boil when I prepare my coffee (using a [French press][1]), and I'm wondering if there's no good reason to do that.

For what it's worth, the kettle has a top (so I'm ruling out dust as a concern), and the water I'm boiling is tap water that's been through a Brita filter in a jig.

If the taste is different, what's the chemical or physical justification? [1]: http://en.wikipedia.org/wiki/French_press