Help Wanted - Low Water Alarm PUBLIC

Low Water Alarm for Caravan Water Tanks

This circuit is (hopefully) a Low Water Alarm for double water tanks on a Caravan. Each tank circuit has a seperate LED triggered when the water level drops below the sensors (shown here as 2 wires terminating without connections) - the idea being that once the water level drops below the level of the bare wires, the resistance will increase to greater than the 100 ohm resistor and trigger the BC547 transistor to complete the circuit for the LED and trigger the 2nd transistor to complete the circuit for the Buzzer. The Buzzer is shared between the 2 circuits - not sure if this will work? I'm wondering if I need to fit diodes to prevent any stray voltage working "backwards" into the circuit and stuffing things up (apologies for my lack of correct terminology) . These circuits also have connections to a solenoid on each water tank to shut the water flow when switch is off and open when switch is on. Everything designed to run off 12V, so some of the components shown on the diagram may not be compatible - but the parts purchased are all correct for 12V, so should work fine.

I am completely new to circuit design, so have no idea if this will work, or what I need to do to make it work? Have just purchased breadboard to test this design - guess I'll find out????? All comments welcome.