In Proteus Stephen imagines his uncle Richie Goulding saying "Damn your lithia water," and in Sirens Miss Kennedy puts a teatray on an "upturned lithia crate." Lithia water was a kind of bottled mineral water popular at the turn of the 20th century.
Much of this water came (and still comes) from Lithia Springs, Georgia in the U.S. The lithium salts in the water were supposed to cure various ailments, and doctors prescribed it for their patients. In 1888 a resort spa opened in Lithia Springs, and the water also began to be bottled and sold.
When Richie Goulding says (in Stephen's imagination), "Damn your lithia water. It lowers," it is not clear whether he is referring to some preference of Stephen's or whether he is using "your" in a generic sense. Nor is the sense of "lowers" made very clear. Does lithia water lower one's metabolism? one's spirits? the strength or flavor of one's "malt"? The OED notes that "lower" can mean "to dilute." It offers several examples, including one from Dickens' Martin Chuzzlewit: "What do you go a lowerin' the table-beer for then?"
It seems most likely that Richie is rejecting the theory that "Whusky" should be diluted with a drop of water, and especially mineral water. In "A Little Cloud," Ignatius Gallaher greets his old chum with a discussion of the issue: "Hallo, Tommy, old hero, here you are! What is it to be? What will you have? I'm taking whisky: better stuff than we get across the water. Soda? Lithia? No mineral? I'm the same. Spoils the flavour. . . . Here, garçon, bring us two halves of malt whisky, like a good fellow."