We're absolutely guilty of this: letting the shower run until it warms up. So we were pretty excited when we spotted this small and cheap device that stops shower water from funneling down the drain...
In turns out, in those morning minutes while you're waiting for the shower to heat up, you're wasting two-and-a-half gallons of water a minute.
Evolve makes an adapter that senses when the water is hot, then stops the water flow down to a trickle. When you're ready to get in, you pull a cord and water pressure--and warm water--resumes.
They also make low flow shower heads with the same adapter. While we're usually pretty good about checking the water temperature, it's nice to think we wouldn't be wasting any water if we did get sidetracked.