Colorless liquid

In the experiment class, the teacher puts two transparent and immiscible colorless liquids in a flask, and then said to the students: “One of the liquids is known to be water, but I don’t know which layer it is on. , Can anyone of you think of a simple way to distinguish?"

[Reference answer]

Add a little more water to see which layer the water settles on, then the water is on that layer.