Of my favorite subjects to photograph, waterfalls rank near the top. I prefer to render my waterfall photographs with the "silky" look to the water. This requires using a tripod and selecting a long shutter speed; usually 1/4 second or even longer depending on the amount of light available and the chosen aperture. A day with no wind or breeze is optimum because moving leaves will show up as a ghost image when using long shutter speeds. If you can't achieve a long enough shutter speed a neutral density filter over the camera lens will help.