Schematics for device, which reacts to water?
Here is a simple way to trigger a sound output whenever the moisture sensor's resistance drops to the 1 M range:







simulate this circuit &ndash; Schematic created using CircuitLab


When the sensor resistance is effectively infinite, the 2n7000 gate will be pulled low, hence it will not conduct. 
As the sensor resistance drops towards the 1 M range, the voltage at the gate will be pulled higher, to the point where the MOSFET begins to conduct. 
At this point, the piezo buzzer will begin to make a sound.


Continuous sound piezo buzzers are inexpensive, and need no additional circuitry: Once they have power, a tone sounds, and continues until power is removed (i.e. MOSFET stops conducting due to sensor drying up).

Such buzzers are available for as little as 50 cents, for instance on eBay, $2.90 for 6 units, with free international shipping.