The use of a jug at the altar is for several purposes. It being earthenware, it’s appropriate for only a few.
The purposes:
- holding the wine before the preparation of the gifts
- holding the water for the lavabo and
- holding the water for the preparation of the gifts
- holding the water for the ablution of the sacred vessels
- holding the water for the washing of feet
- holding the water for a baptism.
Of these, the first 3 are traditionally smaller cruets (holding between 4 and 12 oz), and of thick glass, cut crystal, or precious metal.
A large (1-2 gallon) jug is often used for the washing of feet, but that’s a once-a-year.
A jug for baptisms is not the preferred form, but would also be 1-2 gallons.
In areas where the roman alphabet is uncommon, it’s not atypical for the S to be reversed by accident.
Within the Byzantine Rite, the zeon has its own kettle - it’s hot water, often boiling or nearly so - and is added to the communion cup during the Anaphora (consecration). It’s often earthenware (and just about the only earthenware vessel used in the altar space in the Byzantine Rite). Such vessels are typically 8-12oz, but larger have been used in certain major parishes. (The Precious Blood is raised in temperature to body tem or just above in the Byzantine Rite.) In this particular usage, Earthenware is used primarily for its insulation value.