FortrezZ FTS05US Z-Wave Plus Flood & Temperature Sensor – US; Price: $49.99 (as of 03:07 EST- More info)

Immediately detects water leaks and notifies you within seconds! Use with a compatible Z-Wave Gateway.
Receive notifications directly to your phone when leaks & temperature alarms are detected!
Place sensor directly on the floor next to your water using appliances & fixtures. Common areas to monitor are water heaters, dish washers, refrigerators, laundry machines, and basements floors.