How is this blur effect done
 

Right at 22 seconds in, how does one blur the water and not the rest?

Panglao Island Nature Resort By Ted Ramasola On ExposureRoom

Re: How is this blur effect done
 

Use a very slow shutter speed. Note that the camera isn't moving.

Re: How is this blur effect done
 

You could also do it in post with a mask.

Re: How is this blur effect done
 

Not the same effect - you can see such as rocks through the semi-transparent water in places. With a mask effect you wouldn't be able to distinguish between them, and for something like the waterfall it would be very difficult to generate an accurate enough mask.

You may be able to do something similar in post by averaging over many frames, but far simpler to do it in camera with a slow shutter speed, as Adam suggests.

Re: How is this blur effect done
 

Yep. This was done with a slow shutter. It wouldn't look as good if it was done in simple post. It could be done nicely with compositing or 3D but that's not the level of production where this topic is at...

Re: How is this blur effect done
 

You could use Wide Time in FCP. Since water is the only thing changing, combining frames together will soften the water but, keep the unmoving stuff sharp.