What you need to know before starting your first project
Your 10 First Projects (Hero / UNO R3)
The 37 in 1 Sensor Kit
Learning Components
Your First 10 Projects With The Arduino/HERO Simulator
Code Like A Wizard
Wizard Coding

Water Level Sensor

Water Level sensors can be used in two ways: to measure water level and to detect rain. The sensor used in this video is analog, it has three pins (VCC, GND, and SIGNAL). It uses the resistance of parallel stripes to determine if there is water. If completely dry, the resistance of stripes will be around 1 MΩ. Water is conductive so when applied to sensor it will change the overall resistance of stripes. When connected to an analog pin of Arduino, the minimum value shown on the SIGNAL pin is 0, which means that the sensor is completely dry. If the sensor is completely covered in water, the SIGNAL pin will show 700, which is a maximum value. Connect it with Arduino (as shown in the schematic).

Let s say we need to know when the water level is low in order to refill it. We added one LED which will warn us if there is less than 50% water coverage on a sensor. Kathode of LED goes to GND via 220Ω resistor and Anode goes to digital pin 2.