SACRARIO (piscina, lavacrum). — A small underground cistern covered by a movable stone, located in a corner of a sacred place or of the sacristy, or behind the altar, which communicates with the outside by means of a drainage pipe or ends in an uncemented pit for the absorption of the water.
It serves to receive the water from ablutions, the baptismal water after the administration of the Sacrament, the water in which the purificators and corporals have been washed, and the sacred ashes resulting from the burning of sacred objects (e.g., the cotton wool used in the sacred anointings). All this is done out of reverence for things once blessed or consecrated (Durando, Rat., I, IV, ch. 55). With regard to the East, there is relevant testimony from the 6th century in the following canonical resolution, given by Giovanni Bar Cursos, bishop of Tell-Mahré (519–58): « Aque ablutionia rerum sacrarum in locum decentem, in fossam profundam prociantur et occultentur » (text reported by Hanssens, op. cit. in the bibliography, III, p. 533).
In medieval churches, beside the altar, on the Epistle side, there was very often a niche in the wall called a piscina, artistically constructed with a basin equipped at its base with an opening for the free drainage of the water; it served for the ablution of the priest’s hands after Holy Communion (from the 14th century onward, the ablution began to be drunk). It is prescribed, for example, by the Synod of Würzburg of 1298, canon 3, and by the Cistercian General Chapter of 1601.
In the Middle Ages, the term s. also designated the church, the presbytery, the wall cupboard, or the place for keeping the pyx containing the Holy Eucharist, the sacristy, or the “pastophoria” of the Eastern rite (cf. Didascalia et Constitutiones Apostolorum, II, 57, 3; VIII, 13, 17), and sometimes the book called Ordinarius.