In the example below the photo on the left is shot with a shutter speed of 1/30 second. The photo on the right is shot with a longer shutter speed of 0,8 second, which creates a lot more blur in the water.
A longer shutter speed creates larger white areas in the picture. I prefer water shots where the water is not blurred out completely. Remember that a big white area is very dominating in the frame. Try out a series of shutter speeds from 1/200 sec to 2 sec and decide your preference when you wiew the days' catch on your computer later.