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 all of: the basin in which the priest washes their hands; the ritual that surrounds this action in the Catholic Mass; and the architectural feature or fitting where a basin or place for one is recessed into the side wall of the sanctuary, or projects from it. If this last includes or included a drain, it is a piscina used for washing the church plate and other fittings, though the terms are often confused. In secular usage, it is an obsolete term for any sink or basin for washing hands, especially in a lavatory.
Ablutions before Christian prayer and worship
Churches from the time of Constantine the Great were built with an exonarthex that included a fountain known as a cantharus, where Christians would wash their hands, face and feet before entering the worship space. The practice of ablutions before prayer and worship in Christianity symbolizes "separation form sins of the spirit and surrender to the Lord." Canthari continue to be used in some Orthodox churches, where worshippers also remove their shoes before entering into the presence of God.
In many early and medieval monasteries, there would be a large lavabo (lavatorio) where the brethren would wash their hands before entering the church. St. John Chrysostom mentions the custom in his day of all Christians washing their hands before entering the church for worship. This practice was first legislated in the Rule of St. Benedict in the 6th century, but has earlier antecedents.
Ecclesiastical usage
The name ("I shall wash" in Latin) is derived from the words of Psalm (KJV; in the Septuagint it is Psalm 25), which the celebrant traditionally recites while he washes his: "I will wash my hands in innocence, so will I compass thine altar, O Lord". The washing of hands during the recitation of these psalm verses is of very ancient usage in the Catholic 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 [liturgy of the Eucharist] 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.
Western Rite
In the Roman Rite, the celebrant washes his hands privately before vesting for Mass, perhaps using the prayer (Da, Domine, virtutem). Within the rite of Mass he washes his hands after preparing the offerings on the altar. This is the lavabo ceremony proper. It appears in both the Tridentine and the post-Vatican II forms of the Roman Rite Mass. It probably developed from the need to wash the hands after receiving the gifts brought by the people at the offertory as was used at Rome. In the Gallican Rite the offerings were prepared before Mass began, as in the Eastern Liturgy of Preparation, so in those rites there was no long offertory rite nor need for a lavabo before the Eucharistic Prayer. In the Middle Ages, the Roman Rite actually had two washings of hands, one before and one after the offertory. The first one has since disappeared, and the one which remains is the second.
At High Mass (or sung Mass), in the older rite, and in the more solemn forms available in the newer version, after the offertory, the celebrant incenses the altar and is then incensed himself at the Epistle side (south side of the altar), he remains there while his hands are washed by the acolytes, who ought to 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, in the 1962 rubrics he says the psalm verses: "I will wash my hands among the innocent...", to the end of the psalm (Psalm 25: 6-12 in the Vulgate, which is Psalm 26: 6-12 in the Hebrew). In the newer Mass the celebrant says the prayer: "Lord, wash away my iniquity and cleanse me from my sin" (Psalm 50:2, Psalm 51:2 in the Hebrew).
