After getting the Powermaster 10 up running in HA, I had a spare mc-302e magnet contact with input AUX. So I startet to do a little experiment to see if I could use it as a water sensor in my kitchen under the sink.
I used a pair from a cat5 cable, but you can use any type of cable really, but the trick for a good detection is doing something like this to cover most area and get a warning as early as possible.
I took a knife and rasped along the pair so the copper was visible, then I glued the wires to the floor under the kitchen counter and cabinets. So wherever the water will come in contact with the pair it will trigger short-circuit on the input of the mc-302e.
And it will work something like this.
I choose to use no resistor on the pair. In the configuration of the devises you select input #1 to be Normally Open.
If the input #1 now will trigger you will get alarm on the magnet contact as you simply can give a friendly name in home assistant 