Florida East Coast shipped fresh water into the Keys, ca 1912, in cars that looked very much like this. See Bramson, "Speedway to Sunshine", p 90. (Later on, conventional tank cars were used: same page.)

The pickle cars I'm familiar with had frameworks around the pickle tubs. See Leider, "Pickle and Vinegar Makers of the Midwest", pp 51-73. In principle a stout enough tub mightn't need a frame, but I haven't seen one that way.

So, I'd guess this is a water car.

Al Brown, Melbourne, Fla.