Because, during the existence of the Temple, wine was offered during the
year for a burnt-offering, but on the Feast of Tabernacles they offered
two drink-offerings, one of wine and one of water. Of the other they
made a special festival on the second day of the Tabernacle assemblage,
calling it the Feast of Drawing the Water. It was founded upon the words
of the prophet:--
"And ye shall draw water with joy from the fountains of salvation."