If you leave water in a ceramic, glass, or cup it will start to taste bad after a day or two, even if it’s covered with a lid. However, when we pour water out of a tap into a glass it will taste fine, even though it’s been sitting for days/months in a water reserve tank. Why is this the case?
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Normally, water has a bunch of dissolved gases in it, as well as dissolved minerals that can react with oxygen. Inside the pipe/tank, those gases have nowhere to go and there’s no oxygen to react with, so the water doesn’t really “age”. As soon as you sit it out in the open the dissolved gas mix changes and any reactions that need oxygen to proceed can get going. There’s enough of that going on in most water to change the taste enough to notice.
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Your accustomed to the taste of chlorinated water. When you leave a glass sitting out it de gasses and also the chlorine evaporates out. I actually prefer it.
Water evaporates from the glass over time, potentially leaving a higher concentration of everything else (minerals, chlorine, etc…)
When exposed to air and light, the water in the glass can … well, grow stuff.
The water in the glass can absorb stuff from the air… dust, scents, etc…
So first off the water in your tap isn’t sitting around for months. It came pretty recently from a water treatment facility of some kind and stayed mostly sealed away from air and light and odors and dust until it got to your tap.
As others said, mostly loss of dissolved gases.
Our water company aerates the water as part of the treatment from open reservoir to pipe. Basically a open tank/pond with water forced up, like a decorative fountain.
I can’t really answer the question but I want to point out that this might just be your personal taste preference.
I think the water that comes out of a tap to taste gross. I taste the minerals and dislike it. I like to drink filtered water. In my experience, filtered water that had been sitting out for days in my water bottle taste just fine. I don’t leave water sitting around in cups for days but I’ve drank water that was in a cup from 1 day ago and taste fine.
I also don’t think water that “sits for months in a reserve tank” is comparable to sitting in a cup. Large bodies of water have current flow. The water in that reserve tank is still moving around constantly, way more than the water is moving around in a cup.
Also unless you have a reserve tank in your house, your tap water came from the pipes that came from a water treatment facility – with pipe connections to thousands of other houses. The water is constantly flowing through the pipes and not “sitting around”.
Maybe it’s a combination of smoking the erb’, as well as my preference for strong tasting/spicy foods, but I really don’t think stale water tastes bad. I know it tastes different and generally not as fresh, but it’s sort of like the difference between really good real coffee and instant for me. One is definitely lower quality with some bad notes (e.g. bitterness of instant = staleness of old water), but at the end of the day, if I really want coffee/water, both will do just fine.
My partner can’t STAND stale water and will outright refuse it, whereas I’m fortunate that I can drink shit that’s been left for well over a whole day and not mind at all. Anyone else relate? I don’t have many riveting conversations about stale water habits
Carbon dioxide is absorbed into the water from the air making it acidic.
This phenomenon means that deionised water purifiers need to constantly recirculate the water to keep it pure and ph neutral.
I think you’re misunderstanding the tap water issue. Water isn’t stored for weeks or months in a water tank. It is cycled, generally filling up at night and being used throughout the day. Stagnant water in a distribution system is routinely checked for water quality to make sure it’s fresh and not that much different than what comes directly from a water treatment plant.
Water “fresh” from a tap is also typically [aerated](https://en.wikipedia.org/wiki/Aerated_water), instead of flat. And cold water can hold more dissolved gases. Room temperature water that has been sitting out for awhile usually doesn’t taste as good as cold, aerated water.
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