Question: Why did you add salt to the holy water you blessed on Sunday? (B.D.)
Answer: Salt has preservative and antiseptic properties. While these qualities do somewhat reduce the spread of illness where holy water is shared by a congregation, the use of salt is more symbolic than practical. The water blessed during the Easter and Pentecost Vigils contains no salt at all -- it is actually baptismal water, removed from the font before the Holy Oils are added.
Salt has been employed liturgically since pre-Christian times. All of the Old Testament offerings of first-fruits had to be seasoned with salt.1 Paradoxically, the Prophet Eliseus used salt to sweeten the water of the spring at Jericho.2 It serves as a symbol of preservation from the corruption of sin, of the savor for holy things. In the rite of Baptism it is a token of wisdom.3 Both in holy water and in Baptism, the blessed salt is a symbol of exorcism:
O salt, creature of God ... I exorcise you so that you may become a means of salvation for believers, that you may bring health of soul and body to all who make use of you, and that you may put to flight and drive away from the places you are sprinkled every apparition, villainy, and turn of devilish deceit, and every unclean spirit, adjured by Him who will come to judge the living and the dead and the world by fire.4
In making holy water, the priest separately exorcises and then blesses the salt and then the water. Finally a mixture of the two is made "in the name of the Father, Son, and Holy Ghost." A final prayer speaks to the use of the blessed water "that, through the invocation of [God's] holy name, wherever this water and salt is sprinkled, it may turn aside every attack of the unclean spirit and dispel the terror of the poisonous serpent."5
Q & A NOTES:
1. Leviticus ii: 13.
2. IV Kings ii: 15-22.
3. Cf. Matthew v: 13.
4. Rituale Romanum, "Ordo ad faciendam aquam benedictam."