Timelapse photography with water is great the first time you see it, and then it starts to wear.
The trick is to use a filter in front of your lens. I used a variable ND (Neutral Density) filter here to reduce the amount of light coming into the lens to the equivalent of a night with a full moon.
In the light I had, this meant that I could leave the shutter open for about 6 seconds. The settings I used here were iso 100, 6 secs at f/22. This averaged out the water movement giving it a velvet appearance - I like it in some situations because instead of capturing a snap of the water surface, it shows water ripple trails, showing water movement.
Compare an ordinary ‘snap’ shot of the water (here a small mountain stream water fall) with the long exposure of the same.
Filters can be very expensive - and are produced as a clear/cloudy or dark cap that fits onto your lens. Different filters are produced for different camera types.
If you want to experiment, you dont need to go to that expense though :) you can hold a variety of different mediums in front of a lens to get a similar result - some examples would be colored glass or (if rigid plastic) clear medium with thin washes over them.
Taking pictures at night-time or in very dark conditions can also allow you to do away with the filter. Sometimes a combination of the two - evening and a filter can capture the warm colors of sunset.
I like using a variable ND filter – it allows me to quickly adjust the amount of darkness in the filter (a bit like polarising glasses).
The technique can be overused - sometimes it is just as good to catch the water flowing without time lapse.
(Thanks to +Renee Leach - who asked me how I did this.)