So being able to carry the weight of a sedan in water means that Dwarven drinking habits are reasonable.
God I love DF.
The difficulty is that fortress mode dwarven activity is peculiarly quantized, as a side effect of simulation parameters and scaling factors. You really need to look at seasonal or even annual averages for many things. The useful number here is probably something closer to "how many weight-squares can an average speed and strength dwarf shift over the course of a year"; e.g. if a dwarf can carry a stone weighing X between stockpiles Y travel squares apart Z times per year, comparing the product X*Y*Z to both real-world numbers and other dwarven tasks is reasonable. If this number is drastically out of line, it should be adjusted. However, given that fortress dwarves do far fewer iterations of things over the course of a season than would be otherwise reasonable due to simulation issues, how much a dwarf can manage to accomplish in a single incident (drinking, carrying, whatever) is obviously going to seem unreasonably large when looked at out of context.
Particular difficulties arise when you consider that DF has both an economics and worldbuilding simulation approach that has similarities to grand strategic scale games like Railroad Tycoon, yet also models individual combat at a detail not seen even in most fighting games. DF effectively has (at least) two different simulation "resolutions" and "speeds", but rather than explicitly switching between them, overlaps them in sometimes weird ways. Many times it works a lot better than you might expect, but the potential for Fun tends to be high along the interface.
Topic drift: The trendy thing in large-scale astrophysics simulation these days is automatically adjustable simulation granularity and speed. Basically, when doing something like colliding two galaxies, the computer looks at things on a very broad (low resolution in time and space) level when things are predictable; but automatically "focuses in" with smaller time and space increments in areas that are "interesting". Perhaps that's a feature to look at adding in for DF 2.x