Now that summer is upon us (well here in Australia anyhow), it's important to stay hydrated and with this project by Instructables member C4rmel you can do so while experimenting with your Arduino or compatible board.
The system uses a force-sensitive resistor placed under a base upon which a bottle of water is placed, the size of which is determined by you water needs. Once you've calibrated the full and empty weight with the resistor - the Arduino can indicated your progress with one or more LEDs.
This could also be used to test if someone has been drinking from a certain bottle that perhaps they shouldn't be - or other weight and Arduino projects. For more information, check out the project's Instructable page. And for more, we're on facebook, twitter and Google+, so follow us for news and product updates as well.
If you're looking to simplify using multiple LEDs into one unit, consider the Freetronics RGBLED: full colour module. It includes a bright RGB LED on the top of the board and a WS2801 constant-current, addressable, multi-channel LED driver on the back. This smart module can be daisy-chained, so you can connect a number of these together in a string and drive each of the module colours individually from your microcontroller. For more information and to order, visit the product page.