I think something is missing here. Suppose that water has some unknown property Y that may allow us to do Z. This very statement requires that water somehow refers to object in the real world, so that we would be interested in experimenting with the water in the real world instead of doing some introspection into our internal notion of 'water'. We want our internal model of water to match something that is only fully defined externally.

Other example, if water is the only liquid we know, we may have combined notions of 'liquid' and 'water', but as we explore properties of 'liquid/water' we find it necessary to add more references to external world: water, alcohol, salt water, liquid... those are in our head but they did not pop into existence out of nothing (unless you are a solipsist).