1.As the built-in device generating electricity without the battery and any other power connets to water, LED will emit the light.                                                                                      

2.When water flows down,the LED will light instantly and automatically by the water temperature;
A. When the water temperature is ≤39c, 
   Blue will show automatically;
B. When the water temperature is between 
    ≥40c, Red color will show automatically;