Many people recommend using different filters (neutral density) when photographing water and waterfalls.  I typically agree with this and have previously done this in practice.  This weekend while out in Canaan Valley in West VirginiaI had the opportunity to go to Blackwater Falls. This is a beautiful little place and just a short walk (192 steps) down to the wonderful waterfall.  I was playing with shutter speeds, exposures, etc trying to get the shot I wanted without having the filters I thought I needed.

Below are the 2 photos taken from the same spot within a minute of each other with different settings.  This will help to show some of the things you can do if you know the details of your shutter speeds and how to alter it.

Blackwater Falls exposer 1/25 sec at f/3.5

Blackwater Falls exposure 1/6 sec at f/19

You can see how the longer exposure make the water stream and flow nicely rather than show every drop coming down.  This is something the the filters will do for you as well without the need to change the settings on your camera.