A lavabo is a device used to provide water for the washing of hands. It consists normally of a ewer or container of some kind to pour water, and a bowl to catch the water as it falls off the hands. In ecclesiastical usage it refers to both the basin in which the priest washes his hands and the ritual that surrounds this action in the Eucharist. In secular usage, it refers to a sink for washing hands; the room in which it is kept is the lavatory.
The name Lavabo ("I shall wash") is derived from the words of Psalm (KJV—in the Septuagint it is Psalm 25), which the celebrant traditionally recites while he washes his hands: "I will wash my hands in innocency, O Lord, and so will I go to Thine altar." He is usually assisted by an altar server who pours the water over his fingers as he says the prayer. This practice is found universally in all ancient liturgical traditions of Christianity. Like most liturgical actions, it has both a practical and a spiritual significance. The practical side is the obvious desire for cleanliness, particularly when handling the bread and the wine for Holy Communion, the spiritual side is found in the words of the psalm which pray for spiritual cleansing, that the celebrant may be found worthy to make the offering. The use of this psalm is first mentioned by medieval commentators.
The washing of hands together with the recitation of these psalm verses is of very ancient usage in the Christian church:
"In the third century there are traces of a custom of washing the hands as a preparation for prayer on the part of all Christians; and from the fourth century onwards it appears to have been usual for the ministers at the Communion Service ceremonially to wash their hands before the more solemn part of the service as a symbol of inward purity.
In most liturgical traditions, the priest washes his hands after vesting, before the beginning of the liturgy. This washing may be accompanied by prayers. Many Christian rites also have the priest wash his hands before beginning the Eucharistic prayer. in the Apostolic Constitutions, VIII, 11, the hands of the celebrants are washed just before the dismissal of the catechumens.
In the Roman Rite the celebrant washes his hands before vesting for Mass, but with another prayer (Da, Domine, virtutem). This is said privately in the vestry. He will then wash his hands again after the Offertory—this is the ceremony that is known as the lavabo proper. The reason for the second washing of hands probably developed from the long ceremony of receiving the loaves and vessels of wine from the people at the Offertory that was used at Rome. In the Gallican Rite the offerings were prepared before Mass began, as in the Eastern Liturgy of Preparation, so there was no Offertory nor place for a Lavabo before the Eucharistic Prayer. In the Middle Ages, the Roman Rite actually had two washing of hands, one before and one after the Offertory. This first one has since disappeared, and the one which remains is the second.
At High Mass (or sung Mass), after the Offertory, the celebrant censes the altar and is then censed himself at the Epistle side (south side of the altar), he remains there while his hands are washed by the acolytes, who must be waiting by the credence table. The first acolyte pours water from the cruet over his fingers into a little dish, the second then hands him the towel to dry the fingers. Meanwhile he says the psalm verses: "I will wash my hands among the innocent...", to the end of the psalm.
A bishop at high Mass wears the "precious" mitre (mitra pretiosa) while he is censed and then washes his hands. A larger silver basin and cruet are generally used for a bishop, though there is no official requirement for this.
I will wash my hands in innocency and I will compass Thine altar, O Lord, that I may hear the voice of Thy praise and tell of all Thy wondrous works. O Lord, I have loved the beauty of Thy house, and the place where Thy glory dwelleth. Destroy not my soul with the ungody, nor my life with men of blood, in whose hands are iniquities; their right hand is full of bribes. But as for me, in mine innocence have I walked; redeem me, O Lord, and have mercy on me. My foot hath stood in uprightness; in the congregations will I bless Thee, O Lord.
After vesting, he goes to the thalassidion (piscina) as washes his hands before approaching the Prothesis (altar of preparation), where he will prepare the bread and wine for the Divine Liturgy. This lavabo takes place quietly, outside of the view of the congregation.
Saint Cyril of Jerusalem mentions a washing of hands that takes place in the sight of the people (Mystagogical Catechism, v). And this still takes place at a Hierarchical Divine Liturgy (i.e., one at which a bishop is serving). He will wash his hands as he stands at the kathedra in the nave of the church. This takes place during the reading of the Little Hours after he has been solemly vested by two subdeacons. The subdeacons and a server will approach the bishop; the server holds the ewer and basin, and has a large towel around his neck. The subedacons pour rose water over the bishop's hands and then lift the towel from the server's neck and give it to the bishop for him to dry his hands. Meanwhile, the Protodeacon is swinging the censer and chanting the verses from Psalm 25. Afterwards, the subdeacons replace the towel over the server's neck, and all three bow to the bishop and return to the sanctuary.
Just before the Great Entrance the same ceremony takes place as during the Little Hours, except now it takes place in front of the Holy Doors of the iconostasis. After drying his hands, the bishop goes to the Prothesis to make his personal commemorations for the living and the dead, as he removes particles from the prosphora.
The clergy will also wash their hands after receiving Holy Communion, but this is not accompanied by special prayers.
Though ecclesiastical lavabos are ordinarily of metal, a familiar lavabo consists of a terra cotta tank with a faucet attached and a small basin below it. Today it is a common feature in many gardens in Europe and the U.S, although as a decoration, whose practical use has been long forgotten.
The lavabo may be considered the forerunner of the modern sink.