This is a result of the large amount of bacteria, dust, and toxins present in air, all of which settle inside the glass of water.

An open glass is susceptible to all sorts of dust particles, toxins or bacteria entering the glass. These can be microscopic and so while it may look ‘clean’ there can be some nasties lurking inside.

Also when water is exposed to air, it begins to absorb large amounts of carbon dioxide, this reduces the pH level of the water and gives it an off taste. Therefore a glass of water that has been left out overnight, doesn’t give the body the same benefits as a fresh glass. On the contrary, it may have a bad effect on the body, because it’s full of bacteria and toxins in the morning. It is therefore recommended to pour out the old water and only drink fresh water, which isn’t contaminated in any way.