It is believed in some doctrines that the use of holy water dates to the first century, some sources relate its early usage to St. Matthew although, written documentation about its usage date to the third or fourth century.
Holy water has been spotted in the Old Testament, where the Jews were known to have ritual ablutions to prepare for worship. The ministerial priests always had symbolic washings with water to prepare for worship in God’s temple. And in the bible the use of holy water was recorded in number 5:17 ‘’Then he shall take some holy water in a clay jar and put some dust from the tabernacle floor into the water.’’
Most Catholics are familiar with the practice of entering the church, dipping the finger(s) of their right hand in the font with holy water, and making the Sign of the Cross. Catholics repeat this ritual on leaving the church as well.
Holy water, its water that has been blessed by a member of the clergy. it serves as a symbol of purification and blessing used in baptism and to bless individuals, churches, homes, sacramentals of devotion. Holy water has been used by religious (both Catholic and Lutheran) churches as a means of removing uncleanness, either ritual or moral.
Traditionally, Catholics use holy water for the purpose of baptisms, blessing of persons, places, and objects, or as protection against evil and danger. In catholic church, Holy water is used by the priest to sprinkle the congregation during the entrance rite of the Mass.
Keep in mind therefore, when the water is blest it is holy indeed. But without faith it serves no purpose for: Hebrews 11:1 says ‘’Now faith is the assurance of things hoped for, the conviction of things not seen.’’