Big Tumbling Creek Falls. Clinch River Valley SW Virginia ©1994
I hear this question so many times: "how do you get that fuzzy soft look to the water?" Very simple.
A tripod is a must. And a slow shudder speed is equally important. A one or two second exposure will do the trick. Even a half second will get you there. This is one time when a blur is acceptable.
If you wish to go to the other extreme and stop every droplet in mid air use a fast shutter speed. Start with about 1/200 and go up from there; bright lighting will get you an even faster exposure. At this speed you can hand hold the camera.