Tractate Berakoth, by , by A. Lukyn Williams, , at sacred-texts.com
M.VII. 8 (5). If there are two companies that are eating in one house when some of them [can] see the others, behold, they join themselves together to give the invitation [to say the Benediction]. But if not, then they give the invitation each party to themselves.
They do not say the Benediction over the wine until one puts water into it. This is the opinion of R. Eliezer. 3 But the Majority say: They say the Benediction.
64:3 R. Eliezer. His reason was that until water was mixed with the wine there was some doubt whether it was drunk (cf. p. 45). The Majority assume it would be. The fact that our Lord spoke a Benediction over the wine at the Last Supper (Mark 1423; Matt. 2627; Luke 2217; and apparently 1 Cor. 1123-25). This supplies no evidence that water had been already mixed with it, if He followed the opinion of the Majority.