Flow sensor

Thank you for the reply!

It seems like the level shifter route will be best?

I just realised I need to connect a JSN-SR04T waterproof ultrasonic sensor also (Operating voltage : DC 5V). I have to work with the Mini Pro 3.3V.

Seems like this level converter will work:
https://learn.sparkfun.com/tutorials/using-the-logic-level-converter