There are many aquarium water level sensors which are water safe and can be wired to any of many devices to send an alert. Some cost less than $20 for the sensor itself, although you’d still need the zwave components.
That said, I wouldn’t use them directly in a dog bowl, since the dog might try to play with the sensor.
Instead, you could set up a closed tank reservoir that fills the bowl and put the sensor in the reservoir. The dog couldn’t get to it, and you’d have more time to do the refill.