The W could be an upside down M, and/or vice versa. As others indicated, the W could stand for "Water". Interestingly, the Hebrew letter "Mem" means "Water"... more M / W interplay.
Mem is also associated with the 23rd path on the Tree of Life, the path of the Hanged Man. Again, more "upside down" symbolism.
The Ace of Cups is often depicted as the Holy Grail, the cup from which Jesus drank Wine at the Last Supper, and which caught his blood when he was sacrificed on the cross. Another "cross"-reference to the Hanged Man.
Very enlightening how these symbols flow into one another...