First, the good news. Pure water molecules don’t go bad. They’re just H₂O—no expiry date needed. Water is immortal in a chemical sense.
But your plastic bottle? That’s a whole different story. The real villain here is time and plastic chemistry.
How Long Is "Officially" Okay?
Most bottled water has a “best by” date of 1 to 2 years. That’s not for the water—it’s for the bottle. Over time, plastic can leach tiny amounts of chemicals into the water. It’s not dangerous in small doses, but it might taste a bit like a swimming pool.
After about two years, the water can start to taste flat or musty. Why? Because carbon dioxide from the air slowly creeps in, making it taste stale.
