No extra hardware required (with Proton at least)
With 100k resister between A1 and ground. Use 2 wires from +3.3 and A1
analogRead(A1) = around 37, touching both wires gives around 140, clean tap water = 1800
pinMode(A1, INPUT);
water = analogRead(A1);
if (water > 500) // make this value lower for more sensitive or higher for less sensitive.
{ // water, water, everywhere!}
I use a plastic bottle cap sitting on a paper towel to monitor my basement floor.
