Matthew Poole and continuators on John 2:6

6 And there were set there six water-pots of stone after the manner of the purifying of the Jews, containing two or three firkins a piece .

The Iews were wont in their Dining rooms, to have Water-pots standing; whether one for every guest, (upon which account some think here were six) doth not appear.

For, the content of these Vessels, it is uncertain; the reason is, because the Jewish measures, both for things dry and liquid, are much unknown to us, most Countreys varying in their measures. According to our measures, these Vessels should contain three Hogsheads, or near it; but it is not probable that so great Vessels of Stone should stand in a room; the end of their standing there, was for the people to wash in, before they did eat, Matth. 15.2. Mar. 7.3. and to wash their Vessels in, v. 4. We are certain of the number of the Vessels, but not of the content of them. Some say, they held so much Water, as being turned into Wine, was enough for 150. Persons; but we can make no certain Judgment of it.