If you zoom out far enough, there's a single amount of water on the planet that never changes. Zoom in a little bit, and that single amount of water is unevenl

If you zoom out far enough, there's a single amount of water on the planet that never changes. Zoom in a little bit, and that single amount of water is unevenly distributed but still part of a cycle that is global in scale. Zoom in a bit more, and it's extremely unevenly distributed and a part of regional cycles in which it is relocated in the short term but restricted in the long term. Zoom in a bit more, and it's extremely unevenly distributed and a part of local cycles, where it never leaves a watershed (for example). Which zoom level(s) you choose depends on your purpose and your agenda.