How true this is... I love how my girlfriends' never get it... they think I'm just 'doddling.' Little do they know that if I had enough time (and a big enough hot water heater)... I'm sure my thinking in the shower would facilitate my destiny to conquer the world.
Then I, for one, welcome our new wrinkly-pink overlords.
Shower ideas are great, but taking long showers to get ideas is criminally wasteful. Try this instead: go into the bedroom, make it really dark, light a candle or something and play one of those 'pink noise' tracks: rainforest, ocean, etc. Or take a walk.
If you're not actually cleaning yourself--that is to say, if you're already clean, not if you're lazy--then there's no reason to be using any more clean water. There could be set up a switch that, when flipped, moved from a "use/dispose" model to a "use/recycle" (under the literal meaning of the term "re-cycle") one. It would, of course, build a small buffer at the beginning so it wouldn't just be spraying the last of your shampoo all over you, but that would be the last of the new usage for the day, and it could last as long as you want--only as dirty as a bath, but in motion!
You're in luck, there's a deep shelter tunnel complex under the heart of London, below the underground, up for sale right now, complete with generators, artesian well, room to sleep 8,000 people...