Mopeka also makes a lesser known water tank sensor. It looks very similar to the propane sensors so I would think adding support would just be a matter of getting units correct.
I will be getting mine in soon and can test.
Here is a link to the page they sell them.
I’m not sure if it was always there, but I noticed you can setup the water tank sensors as well, but they are not auto discovered, you have to go in and click add and select each one. I do wish HA would automatically calculate the percentage of each tank like the esphome integration does for propane.
Propane tanks are standard sizes while water tanks are not. That is most likely why its not an option with water tanks.