In other words, it was never filled to maximum capacity. It appears that it was customarily filled to only two thirds of its capacity.
بكلمات اخرى ،‏ لم يكن الحوض يملأ قط بالكامل ،‏ بل جرت العادة كما يبدو ان يُعبّأ ثُلثاه فقط .‏