Usually while taking water streams/falls camera would let you freeze the action, by using the widest shutter and the shortest exposure (something to the tune of f/2.5 and 1/125s). Just try a little longer exposure and that'll give a much smoother / nicer pic. I saw this initially in Dan Heller's site (danheller.com) and tried it for couple of pics. Was initially trying to use exposure times of about 2-4 seconds, but soon realized something like 1/8 seconds is more than enough. In most practical cases, this is all that is possible with the thinnest shutter width (f/32 in my camera / lens).

In the first pic of the stream, taken near Mullodi village @ the foot hills of Kudremukh, the settings used is f/32 and 1/8 sec, to give a smooth / continuous effect to the stream. The small 'f' value also ensures that the whole frame is easily focused.

The comparison picture just shows the difference of using longer exposures. Left side uses f/2.5 and 1/125, while the right side uses f/16 and 1/3 seconds. Btw ... the higher exposure pic may get blurry without a tripod or atleast a support!