When I tested the water detection circuit for my Home Environmental Sensor Array at the Makerspace yesterday, I used distilled water from a water bottle. That is probably why the pi did not detect a current.
I setup the HESA at home and tried some water from our well. At first, the HESA did not detect any electricity. I left the leads in the water for a few minutes and it suddenly worked! The HESA detected the current and shut off the light I connected to the outlet. After that, the circuit always detected the current. Maybe the water needed to get a bit electrified first.
Next, I got some water from the crock that I eventually want to put the sensor in. That water should have more saline and iron in it making it a bit more conductive. The HESA took a minute to work in that water as well but after a few minutes, the circuit worked and very consistently.
So, I'm feeling better that the circuit will actually work as designed.
Now, I can focus on the PCB and enclosure.