It's a nice teardown, and you can't beat that quiescent current.
I looked at designing a water-detector that could tie into your home alarm system.
For that you need a switched contact output and 12V DC power is available.
The water-sensor's electrodes are touching a concrete floor, so you get false-trips due to noise on ground (loop) between the floor and the mains utility ground.
George Risk Industries already makes a huge line of alarm and water sensors, so I gave up