Obj. 3: Further, bread and wine are the matter of this sacrament. But nothing is added to the bread. Therefore neither should anything be added to the wine.
On the contrary, Pope Alexander I writes (Ep. 1 ad omnes orth.): "In the sacramental oblations which in mass are offered to the Lord, only bread and wine mixed with water are to be offered in sacrifice."
I answer that, Water ought to be mingled with the wine which is offered in this sacrament. First of all on account of its institution: for it is believed with probability that our Lord instituted this sacrament in wine tempered with water according to the custom of that country: hence it is written (Prov. 9:5): "Drink the wine which I have mixed for you." Secondly, because it harmonizes with the representation of our Lord's Passion: hence Pope Alexander I says (Ep. 1 ad omnes orth.): "In the Lord's chalice neither wine only nor water only ought to be offered, but both mixed because we read that both flowed from His side in the Passion." Thirdly, because this is adapted for signifying the effect of this sacrament, since as Pope Julius says (Concil. Bracarens iii, Can. 1): "We see that the people are signified by the water, but Christ's blood by the wine. Therefore when water is mixed with the wine in the chalice, the people is made one with Christ." Fourthly, because this is appropriate to the fourth effect of this sacrament, which is the entering into everlasting life: hence Ambrose says (De Sacram. v): "The water flows into the chalice, and springs forth unto everlasting life."
Reply Obj. 1: As Ambrose says (De Sacram. v), just as Christ's sacrifice is denoted by the offering of Melchisedech, so likewise it is signified by the water which flowed from the rock in the desert, according to 1 Cor. 10:4: "But they drank of the spiritual rock which came after them."
Reply Obj. 2: In Baptism water is used for the purpose of ablution: but in this sacrament it is used by way of refreshment, according to Ps. 22:3: "He hath brought me up on the water of refreshment."
Reply Obj. 3: Bread is made of water and flour; and therefore, since water is mixed with the wine, neither is without water. _______________________
SEVENTH ARTICLE [III, Q. 74, Art. 7]
Whether the Mixing with Water Is Essential to This Sacrament?
Objection 1: It seems that the mixing with water is essential to this sacrament. Because Cyprian says to Cecilius (Ep. lxiii): "Thus the Lord's chalice is not water only and wine only, but both must be mixed together: in the same way as neither the Lord's body be of flour only, except both," i.e. the flour and the water "be united as one." But the admixture of water with the flour is necessary for this sacrament. Consequently, for the like reason, so is the mixing of water with the wine.
Obj. 2: Further, at our Lord's Passion, of which this is the memorial, water as well as blood flowed from His side. But wine, which is the sacrament of the blood, is necessary for this sacrament. For the same reason, therefore, so is water.