Hi Nikita,
There are so many examples in the site under the electronic circuits section, here are few links;
http://www.engineersgarage.com/electronic-circuits/water-level-controller-cum-indicator
http://www.engineersgarage.com/electronic-circuits/water-level-indicator-with-display
http://www.engineersgarage.com/electronic-circuits/water-level-indicator-display-gates
http://www.engineersgarage.com/electronic-circuits/water-sensor
http://www.engineersgarage.com/electronic-circuits/tank-full-alarm-circuit