This Water Level Sensor uses an ATTINY45 microcontroller to sense water level in a tank and flashes LEDs to indicate the level of water in the tank.
The embedded video is self explanatory and I'm just using this instructable to upload the Arduino code and the Fritzing sketch that includes the breadboard layout and the PCB design.
The sensor uses an LM 7805 voltage regulator to reduce the 9V battery to 5V for the microcontroller. ATTINY45 analog pins A1, A2 and A3 are used to sense the voltage caused due to presence of water between the pin and the +5V line. Pins 1 and 2 are digital pins and are connected to the signalling LEDs.