I was showing my nephew my Home Environmental Sensor Array over the Thanksgiving holiday. We tested it at his house with his city water. It took about a minute to detect the current but it eventually did.
My nephew did some research and came up with a potentially better and simpler circuit. It basically sends power out through on of the Raspberry Pi's GPIO ports and looks for a signal on another port. There is a resistor on the input side that connects to ground. This stops the pi from getting false readings.
When we tested it out, the circuit never gave a false reading when connected to the resistor. It also detected the current in his water immediately every time. I'll have to solder up another circuit board and test it out at the Makerspace.
I don't understand why the circuit works to block transient current. Maybe someday...
Here is the circuit that I documented using Digikey's Schemeit.