Question
What is the symbolism and background concerning the water that is added to the wine just before the consecration at Mass? Why not just wine? Why was this added to the ritual?
--Wondering in Wheaton
Answer
At one time people made their own wine and brought it to the service. Wine was cut with water to take away the strongness of the alcohol and the "home brew." It was also customary for this to be done for non-religious services.
Later on, around the 4th century, people, like Theodore of Mopsuestia, started to allegorize the Mass and give a meaning to each part of the eucharistic liturgy [and other liturgical items]. He felt that it symbolized the blood and water that flowed from Christ's side after the crucifixion. It has been continued because of this symbolic meaning and others.