No way to do that at present - might be possible with some fairly involved workaround, e.g. having two water objects, slightly offset. Top one would be as it is at present, and that object can be added to the Exclude list from the light creating the reflective caustics, that way it won't create reflective caustics (or refractive caustics, or indeed be affected by that light at all). The second water object would have its reflectivity modified to zero, and would not be excluded - with reflectivity 0 it won't create reflective caustics, just refractive.
Don't know if that would work. Gets even more tricky if the reflective water has to catch the light source, e.g. sun glinting on the water, as then you'd need to add some geometry with non-emitting Light Material to let that be captured in reflections without generating reflective caustics. Or have two Suns, with one set to not generate caustics and only illuminate the reflective water (an Include list for that).