Hello Jace!
I think you are mixing up some here. Eve Water Guard can act as a trigger. When water is detected the trigger fires and it could shut off a washing machine that is attached to an Eve Energy - this can be done.
What you want to do: Use a HomeKit enabled contact sensor as a trigger and Eve Water Guard in a scene to be executed.
This is not possible, sorry. Eve Water Guard alarm is for the accessory only.
Best regards, volker
May 8, 2020