chef .... U already know the answer
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a lot and yes. Really shouldn't make much of a difference with soil plants, as the action of watering pulls fresh air down into the rootmass. With hydro, it is a little more important. H2o temperature affects o2 absorbtion, colder water temps hold more oxygen (this is one reason why a chiller is good for hydro)
t ... With ro water, you don't need to let it sit. The whole reason for letting it sit is to let the chlorine evaporate off. Ro removes all chlorine/chloromine.
Another trick to neutralize chloramine is to use ascorbic acid *vitamin c*. Adds some micros too. The half time of reaction between ascorbic acid and chloramine is about 4 min. 1gram to 40gals roughly. Otherwise, it takes @ 24hrs of sitting out to breakdown (high intensity light can help too)