Here is a tested Arduino project that uses 3 sensor probes as water level indicator with 3 ... that is turning ON when the water level is HIGH. This can be useful when you want to empty the tank once ...

IC1 (ofcourse with pre-loaded Arduino UNO Bootloader) can be programmed/re-programmed through the serial interface socket J3 using a commonly available FTDI Basic board (usb-serial converter board).

[Raikut] made this process a lot easier by designing an LED bar indicator to monitor the water level. The sensor is very simple ... linear regulator into the tank. The base of each transitor ...