First of, yes I do realise that if they could, it would look very much like waterbending.
Secondly, sorry if this is a silly question, but I was just idly wandering about how infusing something with stormlight to alter its gravity works. Does it have to be a solid, clearly defined object like a rock (or a person)? If Kaladin tried to infuse liquid, would the stormlight just, well, spill through it, or would the lashing work? In other words, if he was trying to put out a fire, could he move just the water out of the water barrel, or would he have to take the barrel as well?
Has Mr. Sanderson answered this somewhere?