Vidi aquam

Vidi aquam is the name of an antiphon, which may be sung during the Latin Rite Catholic Mass. It accompanies the Asperges, the ritual at the beginning of Mass where the celebrant sprinkles the congregation with baptismal water.
It is sung from Easter Sunday throughout the liturgical season of Eastertide until the feast of Pentecost. It replaces the simpler antiphon "Asperges me", which is used outside Eastertide.
The text refers to the words of the prophet Ezekiel (Ezekiel 47:1), who saw the waters gushing forth from the Temple as a sanctifying flood that flows eastward through the earth and purifies the sea.