iShower Timer is a visual timer app that can help you to avoid too long showers and unnecessary waste of water and money.

Simply configure the maximum time you want to spend under the shower, the water flow per minute of your shower head and an optional audio alarm. Then place your iPhone/iPod touch in a visible but dry location in your bathroom, start the timer and enjoy a refreshing shower.
The timer display starts with a green display that slowly changes into deep red. If enabled, a selected audio is played every 15 seconds after the max shower time is reached.

The history function shows your shower behavior and the amount of water spend for each shower.