I’m not an authority on the subject but I would hesitate to do what you’re considering. The probe is nothing more than a Printer Circuit Board made of phenolic resin. This material is not designed to be food-safe. In other words, this material was never designed (let alone tested) to be in contact with solids/liquids you ingest.
For your application, it will be always be in contact with the water you will be consuming. Will the material, or byproducts of the material’s manufacturing process, leach out into the water? I can’t say for sure. I wouldn’t risk it.
Since you don’t exactly need to know how much water it has, you could also use a load cell under the coffee maker. And with proper calibration you could even measure the amount.