I agree completely with Bob F. If the water turns to milk the exposure is way to long. I prefer water to appear as water not as a soft stream of something else.
This can be a wonderful process, but is most often over done by picture makers today. So many people today see a an old technique that originally occurred by necessity not a trick. they immediately want to copy it as something new and different. They think I have got to try that! But usually when they get the chance they way over do it. Go ahead and try it but use some common sense.
Water in no way appears in my life the way it is depicted by some photographers. The blurring water captured by the long exposures necessary to make any image in the early days of picture making was not then nor is now in my opinion considered to be a work of fine art!
This post in no way is intended as criticism of any one person who prefers "silkey Milk" to georgous stream water!
It is simply a statement of my preference and opinion.
Shoot short enough to show movement, but not so long as to create the antiquated old time milky look of early camera
I have a bucket of water standing by in case of flames.:-)