Herodotus writes that Cleomene’s madness proceeded from the habit of drinking wine unmixed with water, which he learnt of the Scyths.  Likewise Plato, in Laws, says:  But the Scythians and Thracians, both men and women, drink unmixed wine, which they pour on their garments, and this they think a happy and glorious institution.

 "Alcohol consumption in the ancient world was a matter of public endeavour" Tamra Andrews,  An Encyclopaedia of Food in World Mythology (2000)

An exchange between one of the ambassadors and Dicaeopolis in Aristophanes' Acharnians also illustrates the barbaric nature of the custom:

A: And when we were entertained, we were compelled to drink unmixed sweet wine from cups of glass and gold —

D: City of Cranaus!  Are you aware how these ambassadors mock you?

A variation on this ancient custom is still performed today as part of the Mass, when the priest pours a few drops of water into the wine and says this prayer (Novus Ordo):

By the mystery of this water and wine may we come to share in the divinity of Christ, who humbled himself to share in our humanity.