XP

Bottled water can theoretically be stored indefinitely if it's properly sealed. The only risk being that it'll taste bad due to plastic not being impenetrable on the molecular level. Thus if you want to store water, go for glass containers as they're better in this regard.

But what if it's an opened bottle of water that you've taken a sip from? A human's spit is full of bacteria and can definitely contaminate food.

From a statement of the director of the Department of Water Hygiene at the Norwegian Institute of Public Health: "Very few pathogenic bacteria can survive in clean water. After a while they will simply die out."

Basically; nothing really harmful should be able to develop, but the water will probably taste bad. Also don't spit into your water.. The less bacteria, the smaller the risks.