Hello both!
opps! Maybe I should describe clearly in the first post

Sorry for the confusion guys!
I know this can be done easily by using relay, but I wish to take this chance to learn how to use Mosfet to cut the ignition and water level sensor as well.

anyway, I have tested Mosfet driver circuit on water pump today, and........(drum roll please...)
Nano - fried
Mosfet - fried
Mosfet driver - fried
1) The BJT circuit wont fry anything, but just unable to turn off the water pump, pump keeps running)
2) The Mosfet circuit start the pump and fry everything within 10 sec...Power on, everything were okay, until I start the pump..... I don't even have a chance to measure the Low High voltage.....
So from BJT circuit, seems like the
Mosfet can handle the voltage coming from the cdi to ignition coil.
I though the Mosfet driver will be more reliable??
Thanks both!