The question Why is methanol more acidic than water? deals with the reasoning of why methanol is more acidic than water. However, as mentioned in the comments of that question, the acidity constant of water is 14.0, as confirmed by two sources[1][2], with one of them offering a very convincing explanation. The Wikipedia page[3] for methanol quotes its acidity constant to be 15.5.
So it would seem, water is more acidic than methanol. But an answer to the question mentioned above gives a good reasoning for why methanol is more acidic than water (it doesn't deal with the pKa of water, though). Also, the answer mentions that water would be much worse an acid in DMSO. Another question implies that methanol and other alcohols are more acidic than water.
On the other hand, it is also true that we regard alkoxide ions as being more strongly basic than the hydroxide ion (thus we use them primarily for elimination reactions).
This leaves us in a fix. So what is the ultimate truth?
[1]: What is pKa of water? - Chemistry ChemLibreTexts
[2]: Water (Data Page)
[3]: Methanol
Answer
First, water's pKXa in water is 14 as explained here. This means that HX2O is slightly dissociated in liquid form, such that [HX+]=[HOX−]=10X−7.
Second, I would say that caring too much about which compound is the best acid is a bit like arguing by definition. Acidity is a fuzzy concept used as a shorthand for deeper meaning. This means there is little point arguing about the shorthand when we have the actual properties it synthesizes.
solventpKXa of waterpKXa of methanolInterpretationwater14.015.5water is more dissociated than methanolDMSO31.429.0methanol is more dissociated than water
But what's the point ? You already have the pKXa values, any practical question you might have about the concentrations of theses solutes in HX2O and DMSO is already answerable.
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