Static scenes are simple in HDr, but can we use it for scenes that contain moving water? (e.g. waterfall)
AFAIK, no you cannot do that with one camera.
Even if you have two DSLRs (with exactly the same lens), due to a very slightly viewing angle, you may need some adjustment in Photoshop to overcome potential artifacts.
People use the same technique to capture HDR video, if you search youtube you might be able to find how they set it up to minimize view angle differences.
You can also "fake" HDR with one Raw file, since Raw has more dynamic range than the JPEG output. Simply shoot in raw, output two JPEG from the same RAW, one -2 one +2 then merge as HDR. It will not be as good as separately captured image, since the true dynamic range did not really increase much, if at all.
You can't do it using a multi-exposure technique, but you can if you have a high dynamic range sensor, shoot RAW and then pull the information into an 8 bit range yourself. There are camera's with 12 to 14 EV dynamic ranges out now which used to be the realm of HDR shots. True, it won't be as good as if you did a +/- 3EV split (which would give you 18 to 20 EVs, but it's still pretty wide. It really depends on what your threshold for "HDR" is.
While not HDR in the tone mapping sense, manual exposure blending will often result in a very pleasing result (much in the way that a neutral grad filter allows for a greater dynamic range in a single exposure).
If the object in motion can be properly exposed in a single frame, then you can take any number of additional exposures and blend them in photoshop, masking the single properly exposed frame of the water (or other object in motion) into rest of the images.
Actually, moving water looks just fine in a multiple exposure HDR, provided you take long exposures. The following image is a composite of 3 images taken in daylight at f22 using shutter speeds of 2 seconds, 8 seconds and 25 seconds respectively without an ND filter. So yes, it is certainly possible if you are not attempting to freeze the motion of the water. Since silky water is often desirable anyway, I'd say that moving water makes a particularly good candidate for an HDR image.
You could bring your laptop and connect one of these: