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If I leave a glass of water out over night, I notice that it seems to taste different the next day.

Is this because dust is falling into the water?

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  • Is the water at the same temperature ?
    – Max
    Jan 19, 2018 at 21:11
  • Is your water treated, like in some places tap water is chlorinated? I recall some recipes with high sensitivity ask for tap water to be set out overnight so chlorine can evaporate, dunno if it alters taste though.
    – Megha
    Jan 20, 2018 at 7:48
  • @Megha I use osmotically purified water, so that is not relevant.
    – Drisheen Colcannon
    Jan 20, 2018 at 12:42
  • Not sure if the above comment is irrelevant. We can be very sensitive about taste. Overnight standing might be enough for microorganisms to set (nothing to worry about but surely it is a possibility).
    – Alchimista
    Jan 21, 2018 at 10:12

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There is an easy experiment to see if your water is picking up dust. Simply cover a glass of water with a saucer and see if it tastes the same as a glass left uncovered.

You don't say where your water is coming from. Is this from a public water supply or from a well?

Either way it is possible that either the water is either absorbing gasses or releasing them.

Outgassing

In years gone by in southern Michigan there was hydrogen sulfide in the water which gave the water a rotten egg smell and taste. The hydrogen sulfide would outgas over time.

Water can be naturally carbonated so that carbon dioxide will outgas.

Absorption

It is also possible to absorb carbon dioxide from the atmosphere.

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This article suggests that your glass of water absorbs carbon dioxide, becoming slightly acidic and changing its taste. There are other such articles on the internets. Other chemicals can breakdown and and cause changes, but since you are using purified water, these are probably not the cause. So....I would hypothesize that carbon dioxide is the culprit here, not dust.

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  • Very interesting. That seems plausible. Did not think of carbon dioxide. How come you didn't upvote my question?
    – Drisheen Colcannon
    Jan 20, 2018 at 14:03
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    @DrisheenColcannon because voting is subjective and independent from answering - a user may choose to answer a question but not upvote, or vice versa. Please see the tool tip when hovering over the upvote triangle. (And asking for upvotes is frowned upon, btw.)
    – Stephie ♦
    Jan 20, 2018 at 14:55
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The water tastes differently overnight is not because dust is falling in the water but could rather be that any minuscule amount of dust or other TDS in the water is settling down. If you have ever been to any stream or creek you would have noticed that if you disturb the water the mud at the bottom gets dissolved in the water but if you let the water be still for quite some time it again becomes clear because the dust particles again settle down to the bottom. So this could be happening here and dissolved particles must be settling down to the bottom of the glass thus making water taste different but different taste doesn't necessarily mean bad taste or bad for health water.

Now I'm not sure about your surroundings but if there is no source of dust around and room air is also clean then this could be the plausible reason for water tasting different in the morning.

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