A compact vertically mounted float switch can be mounted at either the top or bottom of a tank (by the supplied 'O' ring and nut) to sense the rise and fall of water level in the tank. With minimal wiring and external components, it can be used to produce a digital signal - HIGH or LOW, depending on the water level. The sensor is supplied pre-wired with wire output leads. This sensor can be used to control a pump, an light, a buzzer, or other device based on the water level in the tank. It can also be connected to a microcontroller like the Arduino/Raspberry Pi to sense the water level in the tank.
Note: NO and NC of this float sensor will depend on the placement of the float sensor.
if you place the float sensor at the top of the tank it is normally Closed and when it detects water and starts floating it is Normally Open.
if you place the floater at the bottom of the tank it is normally open and when it detects water and starts floating it is Normally Closed.
For more details check the working image.