I ran mine for 1.0 second, but also had a ND4 (or maybe 8) to drop the f stop a bit, otherwise it gets over exposed. I tried others up to 5 seconds with no improvement in the water (from my point of view), but they got too bright. Looked good when some one walked across the shot tho.Hi @Dove a fast shutter speed on the Manual mode and a higher ISO Setting should stop the water if you have enough light or even possibly set the dial to the Sports one (usually an icon of someone running) , personally I like the slower shutter speed which gives the smooth look like in @straydingo 's pic on the first page
Having said that, there wasn't enough light in the falls area to try for a sharp quick-shutter shot, so a slow one was the better option. If the sun was shining down there, I would've gone the other way...