Sorry about the slow reply. Currently the Crumble can only sense analogue voltages. As Simon said, the DS18B20 uses a digital signal to communicate. It is on my todo list to support, though. I’ve also got some more sophisticated sensors on “Crumbs” coming soon, here’s the temperature one:
Currently, to meassure the temperature of water, I’d probably use a stainless steel-encased thermocouple (like the one n00dle linked to), with an AD8495 chip (Adafruit do a nice breakout board) to get an analogue voltage.
All the best,