This error → if(water) waterLevel = water.gameObject;
it says it cannot convert it?
It’s difficult to tell what you’re trying to achieve here.
It would help users help you, but stating what it is you’re trying to do with your code 
But the reason you’re receiving the error is that it looks like (what I presume is a int or float variable) into a game object. Additionally, the conditional if statement you’ve used should hold a boolean value, and I’m not really sure if it is in the context.
Elaborating on what you’re trying to achieve with your code, would definitely help