Let's move on to some tips for making beautiful waterfall images.
Use Slow Shutter Speeds. Almost always, you'll be shooting at relatively slow shutter speeds to create the effect of flowing water. Those speeds can range from 1/30th of a second to a minute or even longer. To steady your camera, you must—and I mean must—have a very steady tripod.
Even when your camera is mounted on a tripod, use a cable release or the camera's self-timer to prevent camera shake that might be caused by pressing the shutter release button too hard.
I can't give you an exact recipe for the best shutter speed. It depends on how fast the water is moving and the effect you want to create. My advice is to take several exposures at long shutter speeds and then, when you get home, pick the image you like. Often, you can't judge an image by what you see on your camera's LCD monitor.
The close-up you see here was taken using a shutter speed of 1.6 seconds. The Niagara Falls image was taken at 2.5 seconds. The average exposure in my Iceland HDR sequence was taken at 2.5 seconds. So, you see, shutter speeds vary.