How can I turn off the power to an outlet if a water alarm is triggered?
I just recently paired a leak detector with a power relay for an upstairs laundry.

The leak detector has an output contact that is sensed by the power relay.

Floodstop detector, leak sensor and single valve for dishwasher

Furman power relay

I bought an extra sensor (they connect easily in parallel), so that I had one in the pan and one just outside at the base of the wall.  

No extra wiring is necessary, except for converting your DW to a plug and outlet, all other wiring is supplied 

You don't have to connect the valve if you don't want to, but its extra insurance if a hose leaks.