How is the water libation done? He filled a golden flagon holding three lugim, from the Shiloach. When they reached the Water Gate they sounded a tekiah, a teruah, and a tekiah. He went up the ramp and turned to his left.  There were two silver bowls there. R’ Yehudah says: They were of plaster, but their surfaces were darkened from wine.  Each had a hole like a thin nostril, one wider and the other narrower, so that both would drain out at the same time. The western one was for water; the eastern one was for wine. If he poured [the flagon] of water into [the bowl] for wine, or [the flagon] of wine into [the bowl] for water, he fulfilled the obligation.  R’ Yehudah says: He would pour with one log all eight [days].  To the pourer they would say, “Raise your hand!” For once someone poured it over his feet, and all the people pelted him with their esrogim.

Just as it is performed on a weekday, so it is performed on the Sabbath, except that he would fill an unconsecrated golden barrel on the eve of the Sabbath from the Shiloach, and place it in a chamber.  If they were spilled or uncovered, he would refill it from the laver, for uncovered wine and water are unfit for the Altar.