When you leave a glass of water in the sink in the kitchen before leaving for work, why there are so many bubbles in the glass when we return home? Is it safe to drink “old” water? These are some of the most common questions in regard to water consumption. But there is no reason to worry. The water, in theory, never gets “old.”

The bubbles that appear are almost certainly air bubbles that escaped, as the cold water from the sink is heated and releases the gases dissolved in it. Furthermore, a few hours on the balcony can actually improve the taste of water, allowing the taste of chlorine in the water to dissipate, according to the Environmental Protection Agency(EPA).

A few hours out of the tap does not “age” the water that is clean. Thus, it does not become dangerous for consumption. However, policies on safe storage of water for an emergency, as well as common sense, suggests to cover the glass or container to avoid dust and other contaminants to settle on it.

The State University of Colorado says that when the water is properly stored in clean tanks and closed, it should be good forever. The usual recommendation is to store a gallon of water per person per day in case of emergency. The real danger is to put clean water in dirty tanks.

It is a good idea to use and replace stored water every six to twelve months, says the University, change the water as it “serves as an additional precaution against bacteria or viruses that develop in deposits, which may not have been fully or properly cleaned. “