Overview

Don't hard code the water purifier fuel sources.
I had to look into the code to see that:

Also why are the hydration values set like that ?

Just use a dictionary with keys & values in one single file. It would be much easier to deserialize the data if you do.
Usually you would use items as keys and the values as, well, values...

Why would this feature be useful?

• make the mod more modulable (so people can add their own fuel source for modpacks, mod compatibility, and datapacks).
• more readability (for yourself and other people working on your mod)
• more maintainability (you don't have to change your code whenever you want to add or remove a fuel source)