Unfortunately, none of your requirements are Z-Wave standards. It would be helpful to know which products you actually have though, and what your use case is for the Z-Wave water leak sensor. Researching several devices, it seems the behavior you desire is a common design for leak sensors so maybe you can find another one (see below).
Is there a reason you don’t want to involve HA and use an automation? That would be the easy solution. Maybe you want to avoid using HA in case it crashes, or power goes out? Do you have a battery backup for the valve?
Assuming your device is categorized as a Notification Sensor device type (seems to be the common case for water sensors), then in Z-Wave Plus V2, notification devices are actually prohibited from using Basic Set (“Basic Command Class MUST NOT be supported” says the spec). I don’t see how this makes any sense at all, since devices like water vales are also required to support Basic Set commands.
Groups are device specific, and except for the Lifeline (typically Group 1), are not mandatory. There’s nothing that says “Group 2” has to exist or have any prescribed behavior. The fact that your device sends Basic Set commands is a design specific to that device. It may happen to be the same behavior in other devices, but it’s not part of any standard.
Configuration parameters are also device specific. There’s nothing standard about which settings a device should have.
Finally, there’s nothing in the standard specific to Water leak sensors. There are standardized notifications (Notification CC) for water leak detection, but that notification would have the same problem (states are detected or idle), so Basic Set would work better.
As for other products:
HomeSeer HS-LS100+ supports sending Basic Set via Group 2 and doesn’t make any mention of sending dry commands, only leak detection.
Aeotec Water Sensor 7 Basic and Pro also both support a configurable Basic Set command for leak detected. These are Z-Wave Plus V2 devices, which means it ignores the standard with respect to Basic support.
This Custos water leak sensor can configure Basic Set for leak detection and cancellation independently. These are also ZW+v2 devices, and yet still support Basic.
Depending on where you are trying to detect leaks, and if replacing the valve is an option, both the Custos and Zooz ZAC36 water valves include local wired leak sensors. Of course, if you need remote detection, the wired connections aren’t of great use. These valves look identical, maybe Custos is the OEM, or they share the same OEM. Custos manuals are much more detailed.
Both Custos and Zooz sell bundles with valves and z-wave leak sensors, so you would hope they could work together. According to above, the Custos sensors would work fine with either. It appears the Zooz ZSE42 leak sensors only support on/off or off/on Basic Set commands. You could try sending them an email asking for the feature as a potential customer.