I have it all sorted out except for one aspect. The contact sensor to use.
ZigBee or ZWave? I'm going to use a mini float sensor and wire it to dry contacts.
It's not a stationary thing so I don't want to have that make issues with ZWave mesh. But I'm not really finding ZigBee contact sensors with extra terminals. I suppose I could crack one open and modify it but I'd prefer not.
There are the ZD2102 Z-Wave+ contact sensors. They have an external contact connection point that can be used. That is one I use for some stuff. They are sometimes referred to by the older model name WADWAZ (non-Plus version is the difference I think).
How much chaos do you think I would introduce with having it on something that is moved around? Meaning, when it's picked up and taken to the kitchen to fill, for example
Probably not much. All depends on how you wire them up and the smarts of any associated Rules. They also have a tamper switch.
As an example, I have one in my network cabinet. Main, internal contact is at the front door. But I wired three other contacts in series to the other panels of the cabinet so I know if I left any open. I also have a couple of them mounted at windows with 2 sections that open.
For a water bowl... Maybe have it mounted on whatever holds the bowl. If the internal contact triggers, the bowl has been picked up from it's base (or spilled). If the external triggers, the water is low.
I even have a driver (an old one) for this device that lets you choose which contacts to go off for the main capability. Either, both, etc...
I know someone who built one of these. His was stationary. The float sensor was rigged such that the contact (GoControl WADWAZ-1) was closed when the water level was full. He configured his automation such that a solenoid controlling a water valve would turn on a few hours after the contact sensor was open and would close when the contact sensor closed.
This worked great for a short time (maybe a few months), but then over time, a lot of scuzz (like pond scum) accumulated in the bowl. So he stopped using it.
Yes, there are a number of WiFi sensors out there that could do it, let alone DIY. But if you want to stay with ZigBee or Z-Wave the options are a bit more limited.
If WiFi is OK then, I spotted a couple on Amazon that had wired external contacts. Also, as @Bago said, a DIY should be straightforward.
From my experience with my ESP and LED system... You could wire the contact up to an input. Then you have two options (totally DIY route)... Have the ESP throw a simple bit of HTTP at the Hubitat's port (I think 39501) and make a simple driver to parse it.
OR you could make a driver that polls the ESP on a regular basis for the status.
My ESP WS2812 project does the second. Has a simple webserver running to get update binaries, and receive commands. It also provides HTML and JSON status pages. My driver reads the JSON to update the Hubitat device I created for it, and sends the commands as needed to make changes.
I’d be happy too. Mine is battery powered. I am using a LiPoly battery (I built two - cats and dogs - they’re not conveniently located near an outlet). It lasts 3-4 months before recharging.
So in reality additional features then are:
8) Hook up drain valve that empties bowl once a week...
9) Refill bowl but also add sanitizer from a dispenser... (which will then trigger the drain again to empty it and refill with clean water)...
10) Add a second dispenser to add tooth treatment/dental water additive...
Man... it can just keep going...
11) Add a small thermometer just to make sure the kitties have reasonable water...
12) Add a heater to make their TOO COLD tap water reasonable...
13) Add a small chiller (aquarium-type) to cool the water a touch during summer...