A capacitive liquid sponsor relies on the fact the the capacitance or charge between 2 metal plates will change (in this case increase) depending on what material is between them.
This allows us to create a level sensor that is safe for use with any liquid, this one will be used in a buggy with gasoline (petrol).
One plate is hooked to ground. The other connects to pin 23. There is a 820K ohm resistor from pin 22 to 23. The sensor works by charging the capacitor (the water bottle) and measuring how long it takes to drain through the resistor.
Step 1: Parts
1. A solder-less bread board is strictly not needed but make it a lot easier, especially if you plan to add other stuff later.
2. Arduino, I'm using an Arduino mega but a standard one should have just enough pins.
3. LCD character display.
4. Some odds and ends including some wire and a 1MΩ resistor.
5. A computer, you know, that thing your using to read my instructable with.