The Zooz ZEN16v2 or ZEN17 are also good options for connecting arbitrary sensors via Z-Wave, and the ZEN17 in particular is electrically more flexible (sink or source inputs). That said two water leak sensors will often be cheaper than one ZEN17 with its two inputs. An even cheaper option are door/window contact sensors and desoldering the reed switch to replace it with whatever you want, but it's less convenient for sure. And to wrap it all up, Zigbee devices are often a bit cheaper than Z-Wave.