Water’s chemical structure is a boring, loyal molecule. It doesn’t ferment, curdle, or spontaneously combust. But after you unscrew the cap, you’re inviting the whole neighborhood in.
Your mouth has germs. Your dusty nightstand has dust bunnies. The air has spores. All of them cheerfully dive into that bottle like it’s a pool party.
So no, the water won’t “go bad” like milk, but it can start tasting like ew, dust, and regret. That’s not spoilage—it’s flavor theft by bacteria.
