Thanks to all the people who posted on this thread. I was trying to do the same water leak detection and initially used plain DS10A's but never got enough sensitivity. Inspired by the posted circuits, I ended taking a slightly different route: I already had a couple of those "water bugs" boxes that beep when they sense water. Their water detection circuitry is very simple but very sensitive. So instead of adding the posted circuit to the DS10A I hacked something similar so that when these water bugs go active, they activate the DS10A's.
Very simple, 1 mosfet, 1 relay, 1 diode. If anyone's interested, then let me know and I'll post the circuit and where I connected this to these "water bugs".
I.