Now you can extend that truism about oil and water to water and itself. Water and water don't always mix, either.
The textbooks say that water readily comes together with other water, open arms of hydrogen clasping oxygen attached to other OH molecules. This is the very definition of "wetness." But scientists at Pacific Northwest National Laboratory have observed a first: a single layer of water--ice grown on a platinum wafer--that gives the cold shoulder to subsequent layers of ice that come into contact with it.