On the south side of the apse, in a niche in the wall, there is a double Piscina. (Piscina is a Latin word for basin).

The piscina is of medieval origin, the piscinas pictured here date back to the Norman period, (13th Century). It is though that when two piscinas were set side by side (as at St Mary's), one was reserved for the washing of the Priests hands, whilst the other was used for the cleaning of the sacred vessels (Chalice and Paten).

The piscinas each contain a drain (called a sacranium), which is connected with the earth, to receive the water used for the ceremonies.