In a distant galaxy there is a planet, Twin Earth, that is very similar to Earth. In fact, Twin Earth differs from Earth in only one way: it has no water.
Surprisingly, on Twin Earth, the clear, drinkable liquid that falls as rain and fills the seas is not water. It's a different chemical called "XYZ". XYZ looks, tastes, smells, and behaves just like water; XYZ quenches thirst like water; Twin Earth people drink XYZ. In short, XYZ, although not water, is a chemical superficially just water.