G’day - I can’t keep my nose out of things! Leaving water -
including distilled or de-ionised water “sitting around” won’t
remove the air which is dissolved in it. The only way remove
dissolved air is to boil the water and allow it to cool in a closed
vessel, then use it as soon as you can afterwards. If you have a
good vacuum pump you could use it to de-air water to a certain
extent at room temperature. All “sitting around” will do is to
give the chlorine put in by the water authority time to convert to
hydrochloric acid - though not very much of that will be present.
One uses ‘old’ water if one changes the water in an aquarium, to
allow time for the chlorine to convert, and for air to dissolve
in the water! Which the fish must have of course.
This all seems logical: why don’t the fish die? But I can
guarantee that leaving water lying about DOES reduce bubbles in the
investment significantly, so much so that I keep a 25l tank of
water in the workshop for this very purpose. Any scientists like to