I'm looking to do something similar but for various locations in my parents' basement. What did you use for sensors and power? How about communication to the outside world?
It's actually fairly simple. I used the analog pins, and the sensors were just a circuit with a resistor that would be bypassed by the water. I used the 5V pin on the Duemilanove board to put power through the circuit, and then hard coded the numbers from the analog pins into the main loop.
I would have done a simple setup that allowed the water to close the circuit, but the sensors are very sensitive, and would react to my hand being near them when there was no circuit. I don't know enough about electronics to explain why...
As far as communication goes, I have a simple LED setup, with rows of 5 LEDs indicating the water level.
The easiest way I've found for communication outside is with the ethernet shield. I have some motion sensors that phone home to a central server via a network connection and it works very well. I used a wall wart for those.
I would have done a simple setup that allowed the water to close the circuit, but the sensors are very sensitive, and would react to my hand being near them when there was no circuit. I don't know enough about electronics to explain why...
As far as communication goes, I have a simple LED setup, with rows of 5 LEDs indicating the water level.