Is this a good circuit for detecting current path to ground?
As indicated in the comments, this circuit you propose for water level detection isn't going to work. There are a couple of &quot;water level detecting&quot; circuits and even products out there. I've used a simple npn transistor to detect when water is present on two electrodes but I'll provide you with some better examples.
Also tap water resistance can vary depending on what impurities there are in the water and what distance you measure the resistance. From my experience water resistance can be in the 100's of kilohoms. Just today I measured resistance of container of water with my multimeter where electrodes were placed 12 inches apart, it gave a resistance of at least 300kohm.it may be different where you are and your set up. In any case:
For the first circuit shown, there is a ground electrode at bottom of water tank and another electrode placed at certain level within tank. When water is below the level, the circuit will output 0V. When water reaches level, circuit will output 12V. This circuit is based off the idea of a pnp Darlington pair.

For the second circuit shown, there is also a ground electrode at bottom of water tank and another electrode placed at certain level within tank. When water is below the level, the circuit will output 12V. When water reaches level, circuit will output 0V. This circuit is based off the idea of the complementary feedback pair or Sziklai pair.

Note that for both circuits, they use 12V supply, two transistors and resistor values that I determined based on 330kohm water resistance. The R1 3.3kohm resistor is optional but it prevents too much base current if resistance of water reached a low value. If you use a different supply voltage then the resistance of resistors would need to be changed to give better performance.