Have you heard of a Water Pebble?
The water pebble is a small, disc that is placed near the plughole on your shower and measures the amount of water you use. It can also memorize your usage. During the start of your bath, it flashes a green light. The light will start to turn amber when you’re halfway through the acceptable amount of water then switches to red. While this may not make showers fun, it is an ingenious gadget that will help you save a lot of water during your next shower.