Holy water used with faith and devotion purifies venial faults. Saint Augustine used to say that slight sins are no small thing, because many small objects make a great mass; many drops of water fill a river. Many grains make a lot. What then is our hope? First of all, confession.
Holy water reminds us of Christ who presents himself as living water and instituted baptism for us as a sign of salvation. By using the holy water in us, we renew that blessing received in baptism. Every baptized person is called to be a "blessing" (Gn 12:2) and to bless (Lk 6:28).
Remember that when we bless people, we use signs such as the sign of the cross and holy water with the sole objective of glorifying God for his gifts, asking for his help and warding off the evil one. “Cleanse me with hyssop, that I may be pure; wash me, and I will be whiter than snow.” (Ps 50:9).