Actually anything that conducts a small current will trigger the flood warning. Admittedly, I am not fully aware of the specifics of this particular sensor, but in my experience, most/all flood sensors I've worked with will trigger a flood/water warning when a current goes from a point A to a point B (usually aided by a conducting extra 'component'; being the water)
An easy way to test them is usually just connecting the 2 points with a material that conducts (screwdriver, screw, little metal strip etc.)
Back on topic: any idea when you'll be shipping to other countries as well? I currently can't order any which is a bit of a let-down as I found out that I can't integrate my already owned Plugwise material and the Philips Livingcolors lamps, so right now I am sensor-less (And let's be honest, the sensor integration was one of the reasons why I wanted to back the project
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