My definition is that if it’s something that common sense would call water, it’s water. This is the simple trick that defeats all stupid questions.
In your example, brine isn’t water because it’s brine, you even said that in the example.
And if you add food dye to a glass of water, it’s water but colored. Even with you yourself wrote the example implying that it should be water.
The oil with chalk emulsified in water has nothing to do with milk, what does it matter that it looks like milk. And as you yourself implied, it should not be considered water, but an emulsion of stuff.
And notice how I avoided talking percentages, I simply questioned your own common sense. You didn’t even think about it, and yet your common sense made the solution clear in your examples.
You had to go out of your way for that. Not common sense. It’s still not water.