asperges me domine and vidi aquam are hymns sung before the beginning of solemn or high Catholic Masses in the Tridentine use. Both ceremonies are intended to remind the congregation of their baptism and cleanse them before approaching the altar in worshipping at Mass.

The priest processes through the nave of the church wearing an alb, stole, cincture, and cope in that order. The cope must match the color of the liturgical season. Approaching the altar he genuflects at the altar rail. Then kneeling he chants either "asperges me ..." or "vidi aquam ...". At that point the choir continues the hymn, frequently accompanied by congregants who know the Latin and are enthusiastic enough to sing. Turning to face the congregation, the priest with altar server or acolyte proceeds down the center of the nave sprinkling the congregants with an aspergillium, frequently a bronze rod with a bulb at the end. Having sprinkled the nave the priest kneels again at the foot of the altar and leads a verse and response. This completed, the priest intones a concluding prayer. The priest then goes to his sedilla. His cope removed, he dons his chausible and returns to the base of the altar to begin the Mass proper.

In all seasons except Easter through Pentecost, the Asperges is said. The following is the Latin text with a translation.

This text was pasted from The translation is okay in my opinion, so I have kept it save for modernization of pronouns, correction of the medieval j to classical i in the Latin text, and correction of spelling mistakes.

Priest. Asperges me
Choir. Domine, hyssopo, et mundabor: lavabis me, et super nivem dealbabor. Miserere mei, Deus, secundum magnam misericordiam tuam.
Verse. Gloria Patri, et Filio, et Spiritui Sancto,
Response. Sicut erat in principio, et nunc, et semper, et in saecula saeculorum. Amen

The antiphon "asperges me ... miserere" is repeated again.

P. Sprinkle me
C. with hyssop O Lord, and I will be cleansed; wash me, and I will be made whiter than snow (super nivem). Be merciful to me God, according to your great mercy.
V. Glory be to the Father, and the Son, and the Holy Spirit,
R. As it was in the beginning, is now, and ever shall be (semper), world without end. Amen.

The Vidi Aquam is as follows:

P. Vidi aquam
C. egredientem de templo, a latere dextro, alleluia: et omnes ad quos pervenit aqua ista salvi facti sunt, et dicent: Alleluia, alleluia. Confitemini Domino, quoniam bonus; quoniam in saeculum misericordia eius.
V. Gloria Patri, et Filio, et Spiritui Sancto,
R. Sicut erat in principio, et nunc, et semper, et in saecula saeculorum. Amen.

P. I saw water coming
C. forth from the Temple from the right side, alleluia: and all those were saved to whom that water came, and they will say alleluia, alleluia. Give praise to the Lord, for he is good: for His mercy endures forever.
V. Glory be to the Father and to the Son and to the Holy Spirit.
R. As it was in the beginning, is now, and ever shall be, world without end. Amen.

The antiphon "vidi aquam ..." is repeated.

The following verse, response, and prayer is said after either antiphon.

Priest. Ostende nobis, Domine, misericordiam tuam. (alleluia)
Server(s) or congregation. Et salutare tuum da nobis (alleluia)
P. Domine, exaudi orationem meam.
S or C. Et clamor meus ad te veniat.
P. Dominus vobiscum.
S or C. Et cum spiritu tuo.
P. Oremus. Exaudi nos, Domine, sanctae Pater, omnipotens aeterne Deus et mittere digneris sanctum Angelum tuum de caelis, qui custodiat, foveat, protegat, vistet, atque defendat omnes habitantes in hoc habitaculo. Per Christum Dominum nostrum.
S or C. Amen.

P. Show us, Lord, Your mercy. (Alleluia)
S or C. And grant us Your salvation. (Alleluia)
P. O Lord, hear my prayer.
S or C. And let my cry come unto You.
P. the Lord be with you.
S or C. And with your spirit.
P. Let us pray. Hear us Lord, holy Father, almighty and eternal God; and graciously send Your Holy Angel from heaven to watch over, to cherish, to protect, to abide with, and to defend all who dwell in this house. Through Christ our Lord.
S or C. Amen.