There are different ways that you can shoot moving water:
- Freezing it, at about 1/100 s.
- A little movement, at about 1/10 s.
- Much movement, at about 1 s.
- Foggy, at about 10 s.
The best time for each effect of course varies a bit depending on the scene, and the focal length.
A polarising filter has great effect on water, as light that bounces off water gets polarised. You can use it either to remove reflexionsreflections, or enhance them.
A neutral (ND) filter is useful if you want to get a longer exposure time. A tripod (or any other means of keeping the camera still) is needed for the longer times.