We say the characteristic of water is sunyata, because it is constantly changing, and the way it can change depends on its "Dependencies." if you add heat, water evaporate faster (i.e. changes faster.) if you make it cold, water can become ice (i.e. changes). If you leave it be, it evaporates, just slowly (i.e. changes). So a phenomenon can become the cause of another phenomenon, it can also become the dependency of yet another phenomenon. Everything does exist. But everything is inherently sunyata (i.e. changes all the time depending on their Nidānas.)