Temperance is often shown pouring from jug to jug, here we see her priming the well. In one of Julia Cameron's books she writes about refilling the well, in this case, our own mental and physical and spiritual well.
I'm reminded by this card perhaps those times when I think I'm 'least', when there is no spark or ommph, maybe it is just fallow time, and I'm really rejuvenating. We can't possibly hope to survive going full bore all the time, a look around will show the evidence of blow-outs, hence Temperance.
"Joy, temperance, and repose slam the door on the doctor's nose". ~ Henry Wadsworth Longfellow 1807-1882