After a water heater leak I just made my own. I run my HA on a Raspberry Pi, so I connected the GPIO pins to a current-limiting resistor and some wires that I put in the drip pan of my water heater. I made the two contacts using a screw connector, and hot glued it in the pan. You can also do this with an ESP chip. Additionally, I integrated my smoke detectors through an optoisolator and connected all my hard-wired door and window sensors to the GPIO. It's been working great this way for me.