Piscina. In the pre-Reformation English Parish Church, the Catholic Mass was celebrated several times a day at altars in the chancel and nave. Part of the mass requires the ritual washing of vessels. Most altars had a piscina beside them, which was a basin with a drain set in the wall. Water was poured from a jug over the vessels to wash them; the water drained away into sanctified ground in the churchyard.

Most piscinas were simple affairs, but some were very elaborate, as at Flempton. Some are unusual; a piscina is set in the roodloft stairs at Whepstead. There is one high up on the chancel arch at Bures, and one in a partition wall between two altars at Somerton. Piscinas fell into disuse at the Reformation in England.

In the 19th century, under the influence of the Oxford Movement, an attempt was made to reassert the liturgical integrity of many medieval churches. At this time, piscinas were unblocked, and pressed back into use. Many new ones were constructed in a medieval style, and a fine example can be seen at Flixton St Mary. All modern Catholic churches have piscinas.

Some piscinas have a credence shelf set above them in the alcove. Some piscinas have been converted into cupboards, and may be confused with aumbries. Basins set into the wall beside doors are more likely to be holy water stoups. Piscinas are often associated with an adjacent sedilia.