Until recently I understood these entries to warn against diluting one's drink, but yesterday some of the Nanach told me that it is very clear that the only prohibition is on someone selling the drink, and that in fact makes a lot of sense, so I am no longer certain if there is any reason to be careful from adding water to one's personal drink.
Tuesday, December 6, 2011
Not to mix water into one's drink
Rabbainu wrote in Sefer Hamidos, in the entry of "money" item 67, that a person's "food" (livelihood) become increasingly deficient when he mixes water in his drink. Also in the entry of "officers" item 1, Rabbainu wrote that he who's alcoholic beverage is diluted with water, the officers do not deal with him justly.